#include <iostream>
using namespace std;
int main(){
	int n;
	cin>>n;
	int a[n],b[n];
	for(int i=0;i<n;i++){
		cin>>a[i]>>b[i];
	}
	int min=99999,t=0;
	for(int i=0;i<n;i++){
		if(min>a[i]){
			min=a[i];
		}
		t=t+min;
		min=min+b[i];
	}
	cout<<t;
}
/**************************************************************
	Problem: 1827
	User: admin
	Language: C++
	Result: Accepted
	Time:47 ms
	Memory:2072 kb
****************************************************************/