#include <bits/stdc++.h>
using namespace std;
const int maxN = 100005;
double m = 0, a[maxN], b[maxN], x, y;
bool cmp(float a, float b) {
return a > b;
}
int main() {
long long n, i, j;
x = y = 0;
cin >> n;
for(i = 0; i < n; i ++)
cin >> a[i] >> b[i];
sort(a, a + n, cmp);
sort(b, b + n, cmp);
i = j = 0;
while (i < n) {
x +=a[i];
i ++;
while (j < n && y < x) {
if (m < min(x,y ) - i - j)
m = min(x, y) - i - j;
y += b[j];
j ++;
}
if(m < min(x, y) - i - j)
m = min(x, y) - i - j;
}
cout << fixed << setprecision(4) << m << '\n';
}
