#include<bits/stdc++.h>
using namespace std;
int m[10000],num;
int n,a[100050],b[100050],ans=0,ans1=0,ans2=0;
int gaojin(int s)
{
	int i=1;
	while(s)
	{
	m[i]+=s-10*(s/10);
	s/=10;
	if(m[i]>=10)
	{
		m[i+1]+=(m[i]/10);
		m[i]=m[i]%10;
	}
	num=max(num,i);
	i++;	
}
}
int main()
{
	
	cin>>n;
    for(int i=1;i<=n;i++)
    {
    	cin>>a[i]>>b[i];
    	ans=max(b[i],(a[i]-b[i]));
    	if(ans1<=ans)
    	{
    		ans2=ans1;
    		ans1=ans;
		}
    //	gaojin(ans);
	}
//	ans=min(b[1],(a[1]-b[1]));
	gaojin(ans1);
	gaojin(ans2);
	for(int i=1;i<=num;i++)
	{
		cout<<m[i];
	}
	return 0;
}**~~ _

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#### _ ~~**