#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define all(x) (x).begin(),(x).end()
#define DEBUG
#ifdef DEBUG
#define debug(...) [](auto...a){((cout<<a<<' '),...)<<endl;}(#__VA_ARGS__,":",__VA_ARGS__)
#define debugv(v) do{cout<<#v<<" : {";for(int izxc=0;izxc<v.size();++izxc){cout<<v[izxc];if(izxc+1!=v.size())cout <<", ";}cout<<"}"<<endl;}while(0)
#define debugmp(mp) do{cout<<#mp<<" : { ";for(auto p:mp){cout<<'['<<p.first<<" -> "<<p.second<<"] ";}cout<<"}"<<endl;}while(0)
#define debugset(s) do{cout<<#s<<" : {";for(auto x:s)cout<<x<<' ';cout<<"}"<<endl;}while(0)
#else
#define debug(...)
#define debugv(v)
#define debugmp(mp)
#define debugset(s)
#endif
typedef long long i64;
typedef pair<int, int> pii;

const int N = 1e6 + 10;
i64 n, cnt, c[N], pre[N], suf[N];
double p[N], ans; int t[N];
int m[N];
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    cin >> n;
    for(int i = 1; i <= n; i++) {
        double P;
        int C;
        cin >> P >> C;
        if (!m[(int)(P * 1e6)]) m[(int)(P * 1e6)] = ++cnt;
        p[m[(int)(P * 1e6)]] = P, c[m[(int)(P * 1e6)]] += C;
    }
    n = cnt;
    iota(t + 1, t + n + 1, 1);
    sort(t + 1, t + n + 1, [](int A, int B){return p[A] > p[B];});
    for(int i = 1; i <= n; i++) pre[i] = pre[i - 1] + c[t[i]];
    for(int i = n; i >= 1; i--) suf[i] = suf[i + 1] + c[t[i]];
    sort(p + 1, p + n + 1, [](double A, double B){return A > B;});
    //for(int i = 1; i <= n; i++) debug(i, p[i], pre[i], suf[i]);
    for(int i = 1, j = n + 1; i <= n; i++) {
        if(p[i] < 1e-8) break;
        while(i < n && fabs(p[i] - p[i + 1]) < 1e-8) i++;
        double x = 1.00 / p[i];
        if(j <= i) j = i + 1;
        while(j - 1 > i && x * pre[i] + 1e-8 > suf[j - 1] * (1.00 / (1.00 - p[j - 1]))) j--;
        double y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));
        //if (j > i + 1) {

        j--;
        y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));
        j--;
        y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));
        j--;
        y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));        j--;
        y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));
        j--;
        y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));
        j--;
        y = 1.00 / (1.00 - p[j]);
        ans = max(ans, pre[i] + suf[j] - max(pre[i] * x, suf[j] * y));
        //}
        //debug(i, pre[i], j, suf[j], x, y);
        //std::cout << ans << endl;
    }
    cout << fixed << setprecision(15) << ans << endl;
    return 0;
}

/*


3
0.2 100
0.2 100
0.8 100

*/