#include <bits/stdc++.h>
using namespace std;
const double pi = 3.1415926535897932384626;
const int N = (int)1e5 + 7;
int n;
int r[N], h[N], a[N];
pair<long long, int> x[N];
struct fenwick {
  vector<long long> f;
  int n;
  fenwick(int _n) {
    n = _n;
    f.assign(n + 1, 0);
  }
  void update_max(int pos, long long val) {
    for (int i = pos; i <= n; i += i & (-i)) {
      f[i] = max(f[i], val);
    }
  }
  long long query_max(int pos) {
    long long r = 0;
    for (int i = pos; i > 0; i -= i & (-i)) {
      r = max(r, f[i]);
    }
    return r;
  }
};
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &r[i], &h[i]);
    x[i] = {r[i] * 1ll * r[i] * h[i], i};
  }
  sort(x + 1, x + n + 1);
  int cnt = 0;
  x[0].first = -1;
  for (int i = 1; i <= n; i++) {
    cnt += (x[i].first != x[i - 1].first);
    a[x[i].second] = cnt;
  }
  fenwick fwt(n);
  for (int i = 1; i <= n; i++) {
    long long tp = fwt.query_max(a[i] - 1);
    fwt.update_max(a[i], tp + r[i] * 1ll * r[i] * h[i]);
  }
  printf("%.9lf\n", pi * fwt.query_max(cnt));
  return 0;
}
