haha precision

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <cmath>
#include <set>
#include <stack>
#include <bitset>
#include <map>
#include <ctime>
#include <numeric>
#include <random>


#ifndef M_PI
#define M_PI 3.1415926535897932384626433832795028841
#endif
#define int long long
#define uint unsigned long long
#define double long double

#ifdef TIME
#define start cin.tie(NULL); cout.tie(NULL); cout.setf(ios::fixed); cout.precision(10); ios_base::sync_with_stdio(false);int32_t START = clock()
#define finish cout << "\ntime: " << (clock() - START) / (CLOCKS_PER_SEC * 1.0); return 0
#endif

#ifndef TIME
#define start cin.tie(NULL); cout.tie(NULL); cout.setf(ios::fixed); cout.precision(10); ios_base::sync_with_stdio(false)
#define finish return 0
#endif

using namespace std;


//vector input
template<typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (auto &i : vec) {
        cin >> i;
    }
    return is;
}

//pair output
template<typename E>
ostream &operator<<(ostream &os, pair<E, E> &t) {
    os << t.first << ' ' << t.second;
    return os;
}

//"map" pair output
template<typename E>
ostream &operator<<(ostream &os, pair<const E, E> &t) {
    os << t.first << ' ' << t.second;
    return os;
}

//vector output
template<typename T>
ostream &operator<<(ostream &os, vector<T> &vec) {
    for (T i : vec) {
        os << i << ' ';
    }
    return os;
}

//2 dimensional vector output
template<typename T>
ostream &operator<<(ostream &os, vector<vector<T> > &vec) {
    for (vector<T> i : vec) {
        os << i << '\n';
    }
    return os;
}

struct segtree {
    int n;
    vector<double> tree;

    segtree(int _n) {
        n = _n;
        tree.resize(2 * n);
    }

    void set(int i, double v) {
        i += n;
        tree[i] = v;
        i /= 2;
        while (i != 0) {
            tree[i] = max(tree[2 * i], tree[2 * i + 1]);
            i /= 2;
        }
    }

    double get(int l, int r) {
        l += n;
        r += n;
        double ans = 0;
        while (l <= r) {
            if (l % 2 == 1) {
                ans = max(ans, tree[l]);
                l += 1;
            }
            if (r % 2 == 0) {
                ans = max(ans, tree[r]);
                r -= 1;
            }
            l /= 2;
            r /= 2;
        }
        return ans;
    }
};

int32_t main() {
    start;

    int n;
    cin >> n;
    vector<pair<int, int>> a(n);
    vector<double> v(n);
    vector<int> vv(n);
    vector<double> c(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i].first >> a[i].second;
        v[i] = M_PI * ((double)a[i].first * (double)a[i].first) * (double)a[i].second;
    }
    c = v;
    sort(c.begin(), c.end());
    c.resize(distance(c.begin(), unique(c.begin(), c.end())));
    for (int i = 0; i < n; ++i) {
        vv[i] = distance(c.begin(), lower_bound(c.begin(), c.end(), v[i]));
    }

    vector<double> dp(n, 0);

    segtree sgt((int)c.size() + 1);

    for (int i = 0; i < n; ++i) {
        dp[i] = sgt.get(0, vv[i] - 1) + v[i];
        sgt.set(vv[i], dp[i]);
    }


    cout << *max_element(dp.begin(), dp.end()) << '\n';


    finish;
}