#include <bits/stdc++.h>
using namespace std;
const int LG = 30;
const int MX = 100006;
int gcd(int a, int b) {
  if (a == 0)
    return b;
  else
    return gcd(b % a, a);
}
long long a[MX];
long long d[MX];
map<long long, int> m;
long long tree2[4 * MX], b[MX];
long long query2(int node, int st, int end, int l, int r) {
  if (l > r) return 0;
  if (st == l && end == r) {
    return tree2[node];
  }
  int mid = (st + end) / 2;
  return max(query2(2 * node, st, mid, l, min(mid, r)),
             query2(2 * node + 1, mid + 1, end, max(mid + 1, l), r));
}
void update2(int node, int st, int end, int pos, long long val) {
  if (st == end) {
    tree2[node] = val;
    d[pos] = val;
    return;
  }
  int mid = (st + end) / 2;
  if (mid >= pos)
    update2(2 * node, st, mid, pos, val);
  else
    update2(2 * node + 1, mid + 1, end, pos, val);
  tree2[node] = max(tree2[2 * node], tree2[2 * node + 1]);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int N;
  cin >> N;
  for (int i = 1; i <= N; i++) {
    int r, h;
    cin >> r >> h;
    long long v = (1ll) * r * r * h;
    a[i] = v;
    b[i] = v;
  }
  sort(b + 1, b + N + 1);
  int s = 0;
  for (int i = 1; i <= N; i++) {
    long long v = b[i];
    if (m.find(v) == m.end()) {
      m[v] = ++s;
    }
  }
  long long dist = 0;
  long long res = 0;
  for (int i = 1; i <= N; i++) {
    long long v = a[i];
    dist = query2(1, 1, s, 1, m[v] - 1) + v;
    if (dist > d[m[v]]) {
      update2(1, 1, s, m[v], dist);
    }
    res = max(res, dist);
  }
  double ans = 3.14159265358979323846 * res;
  cout << fixed << setprecision(10) << ans << endl;
  return 0;
}
