#include <bits/stdc++.h>
using namespace std;
template <class T>
T max(T a, T b, T c) {
  return max(a, max(b, c));
}
template <class T>
T min(T a, T b, T c) {
  return min(a, min(b, c));
}
void fastio() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
bool prime[10000005];
void SieveOfEratosthenes(long long int n) {
  memset(prime, true, sizeof(prime));
  for (long long int p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (long long int i = p * p; i <= n; i += p) prime[i] = false;
    }
  }
}
bool isPrime(long long int n) {
  if (n < 2) return false;
  for (long long int i = 2; i * i <= n; i++)
    if (n % i == 0) return false;
  return true;
}
std::vector<long long int> generatePrimeFactors(long long int n) {
  std::vector<long long int> prime;
  for (long long int i = 2; i * i <= n; i++) {
    if (n % i == 0) {
      prime.push_back(i);
      while (n % i == 0) n = n / i;
    }
  }
  if (n != 1) prime.push_back(n);
  return prime;
}
std::vector<long long int> generateFactors(long long int n) {
  std::vector<long long int> fact;
  for (long long int i = 2; i * i <= n; i++) {
    if (n % i == 0) {
      fact.push_back(i);
      if (n / i != i) fact.push_back(n / i);
    }
  }
  fact.push_back(1);
  if (n != 1) fact.push_back(n);
  sort(fact.begin(), fact.end());
  return fact;
}
long long int extendedGCD(long long int a, long long int b, long long int &x,
                          long long int &y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  long long int x1, y1, d;
  d = extendedGCD(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return d;
}
long long int gcd(long long int a, long long int b) {
  while (b) {
    a %= b;
    swap(a, b);
  }
  return a;
}
long long int multiply(long long int a, long long int b, long long int m);
long long int singlemod(long long int a, long long int m);
long long int modpow(long long int x, long long int n, long long int m) {
  if (n == 0) return 1;
  long long int res = 1;
  while (n) {
    if (n % 2) res = multiply(res, x, m);
    x = multiply(x, x, m);
    n = n >> 1;
  }
  return singlemod(res, m);
}
long long int modinverse(long long int x, long long int m) {
  return modpow(x, m - 2, m);
}
long long int add(long long int a, long long int b, long long int m) {
  return (((a % m) + (b % m)) % m);
}
long long int substract(long long int a, long long int b, long long int m) {
  if (a < b) swap(a, b);
  return (((a % m) - (b % m) + m) % m);
}
long long int multiply(long long int a, long long int b, long long int m) {
  return (((a % m) * (b % m)) % m);
}
long long int divide(long long int a, long long int b, long long int m) {
  long long int temp = modinverse(b, m);
  return multiply(a, temp, m);
}
long long int singlemod(long long int a, long long int m) { return (a % m); }
long long int eulerstotientfunction(long long int n) {
  long long int ans = n;
  for (long long int i = 2; i * i <= n; i++) {
    if (n % i == 0) {
      while (n % i == 0) n = n / i;
      ans -= ans / i;
    }
  }
  if (n > 1) ans -= ans / n;
  return ans;
}
long long int ncr(long long int n, long long int k, long long int m) {
  if (k > n) return 0;
  long long int res = 1;
  k = min(k, n - k);
  for (long long int i = 1; i <= k; i++) {
    res = multiply(res, n - i + 1, m);
    res = divide(res, i, m);
  }
  return singlemod(res, m);
}
long long int kadaneAlgo(const std::vector<long long int> &arr) {
  long long int size = arr.size();
  long long int currmax = arr[0], maxsofar = arr[0];
  for (long long int i = 1; i < size; i++) {
    currmax = max(arr[i], currmax + arr[i]);
    maxsofar = max(maxsofar, currmax);
  }
  return maxsofar;
}
long long int getDigitSum(long long int n) {
  long long int co = 0;
  while (n > 0) {
    co += n % 10;
    n = n / 10;
  }
  return co;
}
template <class T>
void printVector(const std::vector<T> arr) {
  for (auto i : arr) cout << i << " ";
  cout << '\n';
}
template <class T>
void printArray(T arr[], long long int n) {
  for (long long int i = 0; i < n; i++) cout << arr[i] << " ";
  cout << '\n';
}
long long int seg_tree[4 * 100005], arr[100005];
void build(long long int index, long long int start, long long int end) {
  if (start > end) return;
  if (start == end) {
    seg_tree[index] = arr[start];
    return;
  }
  long long int mid = start + (end - start) / 2;
  build(2 * index + 1, start, mid);
  build(2 * index + 2, mid + 1, end);
  seg_tree[index] = max(seg_tree[2 * index + 1], seg_tree[2 * index + 2]);
  return;
}
long long int query(long long int index, long long int start, long long int end,
                    long long int qstart, long long int qend) {
  if (start > end || start > qend || end < qstart) return 0;
  if (start >= qstart && end <= qend) {
    return seg_tree[index];
  }
  long long int mid = start + (end - start) / 2;
  return max(query(2 * index + 1, start, mid, qstart, qend),
             query(2 * index + 2, mid + 1, end, qstart, qend));
}
void update(long long int index, long long int start, long long int end,
            long long int pos, long long int val) {
  if (start > end) return;
  if (start == end && start == pos) {
    seg_tree[index] = max(val, seg_tree[index]);
    return;
  }
  long long int mid = start + (end - start) / 2;
  if (pos <= mid)
    update(2 * index + 1, start, mid, pos, val);
  else
    update(2 * index + 2, mid + 1, end, pos, val);
  seg_tree[index] = max(seg_tree[2 * index + 1], seg_tree[2 * index + 2]);
}
bool cmp(pair<long long int, long long int> A,
         pair<long long int, long long int> B) {
  if (A.first == B.first) return A.second > B.second;
  return A.first < B.first;
}
int main() {
  fastio();
  long long int t = 1;
  while (t--) {
    long long int n;
    cin >> n;
    std::vector<pair<long long int, long long int> > arr(n), temp(n);
    for (long long int i = 0; i < n; i++) {
      cin >> arr[i].first >> arr[i].second;
      temp[i].first = arr[i].first * arr[i].first * arr[i].second;
      temp[i].second = i;
    }
    sort(temp.begin(), temp.end(), cmp);
    std::vector<char> v;
    long long int dp[n];
    fill(dp, dp + n, 0);
    for (long long int i = 0; i < n; i++) {
      dp[i] = temp[i].first + query(0, 0, n - 1, 0, temp[i].second - 1);
      update(0, 0, n - 1, temp[i].second, dp[i]);
    }
    cout << fixed << setprecision(9)
         << *max_element(dp, dp + n) * 1.0 * 3.14159265358979323846 << '\n';
  }
}
