#include <bits/stdc++.h>
using namespace std;
long long n, t[1000 * 1000], a[1000 * 1000], b[1000 * 1000], v, ans;
map<long long, long long> w;
long long get(int v, int tl, int tr, int l, int r) {
  if (r < tl || tr < l) return 0;
  if (l <= tl && tr <= r) return t[v];
  int m = (tl + tr) >> 1;
  return max(get(v + v, tl, m, l, min(r, m)),
             get(v + v + 1, m + 1, tr, max(l, m + 1), r));
}
void upd(int v, int l, int r, int p, long long x) {
  if (l == r)
    t[v] = x;
  else {
    int m = (l + r) >> 1;
    if (p <= m)
      upd(v + v, l, m, p, x);
    else
      upd(v + v + 1, m + 1, r, p, x);
    t[v] = max(t[v + v], t[v + v + 1]);
  }
}
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    long long r, h;
    cin >> r >> h;
    b[i] = a[i] = ((r) * (r)) * h;
  }
  sort(b + 1, b + 1 + n);
  for (int i = 1; i <= n; i++) w[b[i]] = i;
  for (int i = 1; i <= n; i++) {
    v = get(1, 1, n, 1, w[a[i]] - 1) + a[i];
    upd(1, 1, n, w[a[i]], v);
    ans = max(ans, v);
  }
  printf("%.7f", ans * acos(-1));
}
