#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 1e5;
const long long MAX_P = 1e15;
const double EPS = 1e-5;
double a[MAX_N + 1], b[MAX_N + 1], sa[MAX_N + 1], sb[MAX_N + 1];
int main() {
int n;
cin >> n;
for ( int i = 1; i <= n; i++ )
cin >> a[i] >> b[i];
sort( a + 1, a + 1 + n );
reverse( a + 1, a + 1 + n );
sort( b + 1, b + 1 + n );
reverse( b + 1, b + 1 + n );
for ( int i = 1; i <= n; i++ ) {
sa[i] = sa[i - 1] + a[i];
sb[i] = sb[i - 1] + b[i];
}
double l = 0, r = MAX_P;
while ( r - l > EPS ) {
double p = (l + r) / 2;
bool isPos = false;
for ( int i = 0; i <= n; i++ ) {
int j = min( (double)n, max( 0.0, (sa[i] - i - p) ) );
if ( min( sa[i], sb[j] ) - (i + j) >= p )
isPos = true;
}
if ( isPos )
l = p;
else
r = p;
}
cout << fixed << setprecision( 4 ) << l;
return 0;
}
