#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
const long long M = 1000000007;
const long double PI = acos((long double)-1.0);
template <typename T>
struct SegmentTree {
  T data[N << 2];
  T calc(const T &x, const T &y) const { return max(x, y); }
  void push_up(int rt) { data[rt] = calc(data[rt << 1], data[rt << 1 | 1]); }
  void build(int l, int r, int rt) {
    data[rt] = 0;
    if (l == r) {
      return;
    }
    int m = (l + r) >> 1;
    build(l, m, rt << 1);
    build(m + 1, r, rt << 1 | 1);
  }
  void update(int p, T val, int l, int r, int rt) {
    if (l == r) {
      data[rt] = val;
      return;
    }
    int m = (l + r) >> 1;
    if (p <= m) {
      update(p, val, l, m, rt << 1);
    } else {
      update(p, val, m + 1, r, rt << 1 | 1);
    }
    push_up(rt);
  }
  T query(int L, int R, int l, int r, int rt) {
    if (L > R) {
      return 0;
    }
    if (L <= l && r <= R) {
      return data[rt];
    }
    int m = (l + r) >> 1;
    T ret = 0;
    if (L <= m) {
      ret = calc(ret, query(L, R, l, m, rt << 1));
    }
    if (m < R) {
      ret = calc(ret, query(L, R, m + 1, r, rt << 1 | 1));
    }
    return ret;
  }
};
SegmentTree<long long> st;
int n;
struct Node {
  long long v;
  int id;
} a[N];
bool cmp(const Node &a, const Node &b) {
  return a.v < b.v || (a.v == b.v && a.id > b.id);
}
int main() {
  while (~scanf("%d", &n)) {
    for (int i = 1; i <= n; i++) {
      long long r, h;
      scanf("%I64d%I64d", &r, &h);
      a[i].v = r * r * h;
      a[i].id = i;
    }
    sort(a + 1, a + n + 1, cmp);
    st.build(1, n, 1);
    long long ans = a[0].v;
    for (int i = 1; i <= n; i++) {
      long long val = st.query(1, a[i].id - 1, 1, n, 1);
      st.update(a[i].id, val + a[i].v, 1, n, 1);
      ans = max(ans, val + a[i].v);
    }
    printf("%.10f\n", double(PI * ans));
  }
}
