#include <bits/stdc++.h>
using namespace std;
double A[100005], B[100005];
int main(){
ios_base::sync_with_stdio(0), cin.tie(0);
int N; cin >> N;
for (int i = 0; i < N; ++i) cin >> A[i] >> B[i];
sort(A, A + N, greater<double>()), sort(B, B + N, greater<double>());
int a = 0, b = 0;
double sa = 0, sb = 0, ans = 0;
while (a < N || b < N) {
if (a < N && b < N) {
if (min(sa + A[a], sb) > min(sa, sb + B[b])) sa += A[a++];
else sb += B[b++];
}
else if (a == N) sb += B[b++];
else sa += A[a++];
ans = max(ans, min(sa, sb) - a - b);
}
printf("%.4f", ans);
return 0;
}
