#include <bits/stdc++.h>
#define int long long
#define ff first
#define ss second
#define pb push_back
#define all(x) x.begin(),x.end()
using namespace std;
signed main(){
ios_base::sync_with_stdio();
cin.tie(0);cout.tie(0);
int n;
cin>>n;
vector <double> a(n),b(n);
for(int i=0;i<n;i++){
cin>>a[i]>>b[i];
a[i]--;
b[i]--;
}
sort(all(a));sort(all(b));
reverse(all(a));reverse(all(b));
double ans=0;
double sum1=0,sum2=0;
int cnt=0;
for(int i=0;i<n;i++){
sum1+=a[i];
while(cnt<n && min(sum1-cnt,sum2-i-1)<=min(sum1-cnt-1,sum2+b[cnt]-i-1)){
sum2+=b[cnt];
cnt++;
}
ans=max(ans,min(sum1-cnt,sum2-i-1));
}
cout<<fixed<<setprecision(4)<<ans<<"\n";
}
/*
4
1.4 3.7
1.2 2
1.6 1.4
1.9 1.5
*/
