#include<bits/stdc++.h>
#define N 100001
using namespace std;
int n;
double a[N],b[N],ans,aans,bans;
bool vis[N][2];
bool cmp(double a,double b){return a>b;}
int main(){
	freopen("wager.in","r",stdin);
	freopen("wager.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++) cin>>a[i]>>b[i];
    sort(a+1,a+n+1,cmp);
    sort(b+1,b+n+1,cmp);
    for(int i=1,j=1;i<=n&&j<=n;){
        if(vis[i][0]==0) aans+=a[i];
        if(vis[j][1]==0) bans+=b[j];
        vis[i][0]=vis[j][1]=1;
        ans=max(ans,min(aans-i-j,bans-i-j));
        if(aans>=bans) j++;
        else i++;
    }
    printf("%.4lf\n",ans);
    return 0;
}