#include <bits/stdc++.h>
using namespace std;
const long double EPS = 1e-9, pi = acos(-1);
const long long N = 1e5 + 5;
long long r[N], h[N], n, F[N], dp[N];
bool cmp(pair<long long, long long> a, pair<long long, long long> b) {
  if (a.first == b.first) {
    return a.second < b.second;
  } else
    return a.first < b.first;
}
void add(long long d, long long id) {
  while (id <= n) {
    F[id] = max(F[id], d);
    id += (id & -id);
  }
}
long long get(long long i) {
  long long res = 0;
  while (i) {
    res = max(res, F[i]);
    i -= (i & -i);
  }
  return res;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (long long i = 1; i <= n; ++i) cin >> r[i] >> h[i];
  vector<pair<long long, long long> > A;
  A.clear();
  for (long long i = 1; i <= n; ++i) {
    A.push_back({r[i] * r[i] * h[i], i});
  }
  sort(A.begin(), A.end(), cmp);
  long long res = 0, id = 0, prev = A[0].first;
  for (long long i = 0; i < n; ++i) {
    if (prev != A[i].first) {
      while (id < i) {
        add(dp[id], A[id].second);
        id++;
      }
    }
    dp[i] = get(A[i].second) + A[i].first;
    res = max(res, dp[i]);
    prev = A[i].first;
  }
  cout << fixed << setprecision(9) << pi * res << endl;
  return 0;
}
