#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 7;
const int INF = 1e9 + 7;
const long long int LINF = 1e18;
const long long int MOD = 1e9 + 7;
using namespace std;
int n;
int r[MAXN], h[MAXN];
vector<pair<long long int, int> > v;
int place[MAXN];
int L[MAXN];
long long int ans;
long long int tree[MAXN];
inline long long int getmax(int x) {
  long long int res = 0;
  for (; x >= 0; x = (x & (x + 1)) - 1) {
    res = max(res, tree[x]);
  }
  return res;
}
void update(int x, long long int new_val) {
  for (; x < n; x = (x | (x + 1))) tree[x] = max(tree[x], new_val);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &r[i], &h[i]);
    v.push_back(make_pair(1ll * r[i] * r[i] * h[i], i));
  }
  sort(v.begin(), v.end());
  for (int i = 0; i < v.size(); i++) {
    place[v[i].second] = i + 1;
    L[v[i].second] = i;
    if (i && v[i].first == v[i - 1].first) {
      L[v[i].second] = L[v[i - 1].second];
    }
  }
  for (int i = 1; i <= n; i++) {
    long long int MX = getmax(L[i]);
    MX += 1ll * r[i] * r[i] * h[i];
    ans = max(MX, ans);
    update(place[i], MX);
  }
  long double ANS = 3.14159265358979323846 * ans;
  cout << setprecision(10) << fixed << ANS;
  return 0;
}
