#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3,unroll-loops")
using namespace std;
#define int long long
#define pii pair<int,int>
#define ff first
#define ss second
#define sp << " " <<
#define all(cont) cont.begin(),cont.end()
#define vi vector<int>
const int inf = 1e17,N = 3e5+1,MOD = 998244353,BL = 1000;
void solve() {
int n;
cin >> n;
vector<double> odds(n),odds2(n);
for (int i = 0;i<n;i++) cin >> odds[i] >> odds2[i];
sort(all(odds),greater<double>()),sort(all(odds2),greater<double>());
vector<double> suf(n+1,0);
for (int i=1;i<=n;i++) suf[i] = suf[i-1]+odds2[i-1];
double ans = 0;
double s = 0;
for (int i=0;i<=n;i++) {
if (i) s+=odds[i-1];
double l = 0;
double r = inf;
double eps = 1e-9;
while (l+eps<r) {
double v = (l+r)/2;
//s-v >= j
int j = min(n,(int)(s-v));
if (j >= 0 && suf[j]-j >= v) l = v+eps;
else r = v-eps;
}
ans = max(ans,r-i);
}
cout << fixed;
cout << setprecision(4) << ans << '\n';
}
int32_t main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#ifdef Dodi
freopen("in.txt","r",stdin);
freopen("out.txt","w",stdout);
#endif
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
