#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
const int inf = 1e5 + 5;
const int MAXM = 1e5 + 5;
const int MAXN = 2e5 + 4;
map<double, int> m;
double v[MAXM], dp[MAXM], tree[4 * MAXM], a[MAXM];
double getmax(int node, int l, int r, int ql, int qr) {
  if (l > r or l > qr or r < ql) return 0.0;
  if (l >= ql and r <= qr) {
    return tree[node];
  }
  int mid = (l + r) >> 1;
  double p1 = getmax(2 * node, l, mid, ql, qr);
  double p2 = getmax(2 * node + 1, mid + 1, r, ql, qr);
  return max(p1, p2);
}
void update(int node, int l, int r, int pos, double val) {
  if (l > r or pos < l or pos > r) return;
  if (pos == l and l == r) {
    tree[node] = val;
    return;
  }
  int mid = (l + r) >> 1;
  update(2 * node, l, mid, pos, val);
  update(2 * node + 1, mid + 1, r, pos, val);
  tree[node] = max(tree[2 * node], tree[2 * node + 1]);
}
int main() {
  int n, i, j;
  scanf("%d", &n);
  double r, h;
  for (int i = 1; i <= n; i++) {
    scanf("%lf %lf", &r, &h);
    double x = r * r * h;
    v[i] = x;
    m[x];
  }
  int k = 1;
  for (map<double, int>::iterator it = m.begin(); it != m.end(); it++) {
    it->second = k++;
  }
  for (int i = 1; i <= n; i++) {
    dp[i] = v[i] + getmax(1, 1, n, 1, m[v[i]] - 1);
    update(1, 1, n, m[v[i]], dp[i]);
  }
  printf("%0.6lf\n", (3.14159265358979323 * tree[1]));
  return 0;
}
