#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
int n;
long long t[200005],s[200005],f[200005];
long long l,r,mid;
void init(){
	cin>>n;
	for (int i=1;i<=n;i++)
		scanf("%I64d%I64d",&s[i],&t[i]);
	for (int i=1;i<=n;i++)
		f[i]=i-n;
}

bool judge(long long tim){
	int i,j;
	i=n;
	while (i>0){
		if (s[i]-f[i]+t[i]>tim) return false;
		if (s[i]<f[i]) {
			tim-=s[i]-f[i]+t[i];
			s[i-1]=f[i]-1;
		}
		else if (s[i]>=f[i]){
			if (s[i]>=f[i]+t[i])
				s[i-1]=s[i]-1-t[i];
			else {
				s[i-1]=f[i]-1;
				tim-=f[i]+t[i]-s[i];
			}
		}
		i--;
	}
	return true;
}
		
void solve(){
	l=0;r=100000000000;
	while (l<r){
		if (l==r-1){
			if (judge(l)) r=l;
			else l=r;
			break;
		}
		mid=(l+r)/2;
		if (judge(mid)) r=mid;
		else l=mid;
	}
	printf("%I64d",l);
}

int main(){
freopen("boarding.in","r",stdin);
freopen("boarding.out","w",stdout);
	init();
	solve();
	
	return 0;
}