#include <bits/stdc++.h>
using namespace std;
using db = double;
int n;
db qsa[100005], qsb[100005];
db ans = 0;
int main() {
cin.tie(0) -> sync_with_stdio(0);
cin >> n;
for(int i=1;i<=n;i++) cin >> qsa[i] >> qsb[i];
sort(qsa+1, qsa+n+1); sort(qsb+1, qsb+n+1);
reverse(qsa+1, qsa+n+1); reverse(qsb+1, qsb+n+1);
for(int i=1;i<=n;i++) {
qsa[i] += qsa[i-1];
qsb[i] += qsb[i-1];
}
int p1 = 0;
for(int i=1;i<=n;i++) {
while(p1 <= n && qsb[p1] <= qsa[i]) p1++;
if(p1 <= n) ans = max(ans, qsa[i] - i - p1);
ans = max(ans, qsb[p1-1] - i - (p1 - 1));
//cout << i << ' ' << p1 << " -> " << ans << '\n';
}
cout << fixed << setprecision(4) << ans;
}
