#include<stdio.h>
int a[200];
int b[200];
main()
{
	int i,n;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d%d",&a[i],&b[i]);
	}
	int t=0;
	int min=999999999;
	for(i=0;i<n;i++)
	{
		if(min>a[i])
		{
			min=a[i];
		}
		t=t+min;
		min=min+b[i];
		
	}
	printf("%d",t);
	
}
/**************************************************************
	Problem: 1827
	User: admin
	Language: C
	Result: Accepted
	Time:68 ms
	Memory:1148 kb
****************************************************************/