#include <bits/stdc++.h>
#define pb push_back
#define ll long long
#define pii pair<int, int>
#define xx first
#define yy second
#define MAXN 100010
using namespace std;
int n;
long double ress=0, a[MAXN], b[MAXN];
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin>>n;
for (int i=0; i<n; i++) cin>>a[i]>>b[i];
sort(a, a+n, greater<long double>());
sort(b, b+n, greater<long double>());
long double aa=0, bb=0;
int i=0, j=0;
while (i<n || j<n)
{
if (i==n || bb<=aa)
{
bb+=b[j++];
}
else if (j==n || aa<bb)
{
aa+=a[i++];
}
aa--; bb--;
ress=max(ress, min(aa, bb));
}
cout<<fixed<<setprecision(4)<<ress<<endl;
}
