#include<bits/stdc++.h>
#define int long long
using namespace std;
struct cow
{
	int x,y,cd=0;
	int grass;
}c[160000];
int cmp(cow a,cow b)
{
	return a.x<b.x;
}
signed main()
{
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>c[i].x>>c[i].y;
		c[i].grass=c[i].y-c[i].x+1;
	}
	c[n+1].x=c[n].y+1;
	sort(c+1,c+1+n,cmp);
	for(int i=1;i<=n;i++)
		if(c[i].y>=c[i+1].x)
			if(c[i].grass>=c[i+1].grass)c[i].cd=1;
	int ans=0;
	for(int i=1;i<=n;i++)
		if(c[i].cd==1)ans+=c[i].grass;
	cout<<ans;
	return 0;
}