#include <bits/stdc++.h>
#define mp make_pair
#define X first
#define Y second
using namespace std;
typedef long long ll;
typedef pair <int, int> ii;
const int N = 1e5 + 1;
const double INF = 1e9;
int n;
double a[N], b[N], dp[N];
void readInput(){
cin >> n;
for(int i = 1; i <= n; i++)
cin >> a[i] >> b[i];
}
void prepare(){
sort(a + 1, a + 1 + n, greater<double>());
sort(b + 1, b + 1 + n, greater<double>());
for(int i = 1; i <= n; i++){
a[i] += a[i - 1];
b[i] += b[i - 1];
}
}
void calc(int l, int r, int from, int to){
if (l > r)
return;
int mid = (l + r) >> 1;
int pos = -1;
dp[mid] = -INF;
for(int i = from; i <= to; i++)
if (dp[mid] < min(a[mid], b[i]) - (mid + i)){
dp[mid] = min(a[mid], b[i]) - (mid + i);
pos = i;
}
calc(l, mid - 1, from, pos);
calc(mid + 1, r, pos, to);
}
void solve(){
calc(1, n, 0, n);
cout << fixed << setprecision(4) << *max_element(dp, dp + 1 + n);
}
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
readInput();
prepare();
solve();
return 0;
}
