#include<stdio.h>
#define mmax 101
#define max(x,y) ((x)>(y)?(x):(y))

int inst[mmax],d[mmax],min[mmax];

int main()
{
	freopen("pachete.in","r",stdin);
	freopen("pachete.out","w",stdout);

	int n,i;
	scanf("%d",&n);
	for(i=0;i<n;i++)
		scanf("%d%d",&inst[i],&d[i]);

	min[n-1]=d[n-1];
	for(i=n-2;i>=0;i--)
		min[i]=d[i]+max(0,min[i+1]-inst[i]);

	printf("%d\n",min[2]-2);

	return 0;
}