#include <bits/stdc++.h>
using namespace std;

int xz[20],n;
double a[20],b[20],ans;

double calc(){
	double cnt1=0;
	for(int i=1;i<=n;i++){
		if(xz[i]==1)cnt1+=a[i];
	}
	double cnt2=0;
	for(int i=1;i<=n;i++){
		if(xz[i]==2)cnt2+=b[i];
	}
	return min(cnt1,cnt2);
}

void dfs(int idx){
	if(idx>n){
		int tot=0;
		for(int i=1;i<=n;i++){
			if(xz[i])tot++;
		}
		ans=max(ans,calc()-tot);
//		cout<<calc()<<"err"<<endl;
		return ;
	}
	for(int i=0;i<=2;i++){
		xz[idx]=i;
		dfs(idx+1);
	}
}

int main(){
	freopen("wager.in","r",stdin);
	freopen("wager.out","w",stdout);
	ans=-INFINITY;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%lf%lf",&a[i],&b[i]);
	}
	dfs(1);	
	printf("%.4lf",ans);
	return 0;
}