#include <bits/stdc++.h>
using namespace std;
long long a[2311];
long long b[2311];
long long c[2311];
int main(){
	int n;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
		c[i]=b[i]-a[i];
		//cout<<c[i]<<" ";
		//cout<<a[i]<<b[i];
	} 
	for(int i=1;i<=n;i++){
		if(a[i]<=a[i-1]){
			if(b[i]>=b[i-1]){
				c[i-1]=0;	
			}else if(b[i]<=b[i-1]){
				c[i]=c[i]+b[i-1]-b[i];
				c[i-1]=0;
			}
			//cout<<c[i]<<" ";
		}else{
			if(b[i]>=b[i-1]){
				c[i]=c[i]+a[i]-a[i-1];
				c[i-1]=0;	
			}else if(b[i]<=b[i-1]){
				c[i]=c[i]+c[i-1];
				c[i-1]=0;
			}
			//cout<<c[i]<<" ";	
		}
	}
	cout<<c[n]; 
	return 0;
}