//#pragma GCC optimize("Ofast,unroll-loops")
#include "bits/stdc++.h"
using namespace std;
#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif
//#define int long long
const int maxn = 1e5+5;
int n;
double a[maxn], b[maxn];
double ps[maxn];
int check(int mid, int argentina, double sum){
double left = min(sum - argentina + 1, ps[n] - ps[n - mid + 1] - argentina + 1);
double right = min(sum - argentina - 1, ps[n] - ps[n - mid - 1] - argentina - 1);
double cur = min(sum - argentina, ps[n] - ps[n - mid] - argentina);
if(cur > left and cur > right) return 0;
else{
if(cur < left) return 2;
else return 1;
}
}
void solve(){
cin >> n;
for(int i = 1; i <= n; ++i){
cin >> a[i] >> b[i];
}
sort(a + 1, a + n + 1);
sort(b + 1, b + n + 1);
ps[n + 1] = 0;
for(int i = 1; i <= n; ++i){
ps[i] = ps[i - 1] + b[i];
}
double ans = 0, sum = 0;
for(int i = n; i; --i){
sum += a[i];
int l = 1, r = n;
while(l <= r){
int mid = (l + r) / 2;
int argentina = (n - i + 1) + mid;
if(check(mid, argentina, sum) == 1){
l = mid + 1;
}
else if(check(mid, argentina, sum) == 2){
r = mid - 1;
}
else{
ans = max(ans, min(sum - argentina, ps[n] - ps[n - mid] - argentina));
break;
}
debug(i, mid, ans);
}
// ans = max(ans, rodi);
}
cout << fixed << setprecision(4) << ans;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int test = 1;
// cin >> test;
for(int i = 1; i <= test; i++){
// cout << "Case " << "#" << i << ": ";
solve();
}
return 0;
}
