#include<bits/stdc++.h>
using namespace std;
int f[200000];
struct qu
{
	int l;
	int r;
}a[200000];
bool cmp(qu x,qu y)
{
	return x.l < y.l;
}
int main()
{
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i].l;
		cin>>a[i].r;
		f[i] = a[i].r - a[i].l + 1;
	}
	sort(a+1,a+1+n,cmp);
	for(int i=1;i<=n;i++)
	{
		if(a[i].r >= a[i-1].l)
		{
			f[i] = max(f[i-1],f[i]);
			if(f[i-1] == max(f[i-1],f[i]))
			{
				f[i] = 0;
			}
			if(f[i] == max(f[i-1],f[i]))
			{
				f[i-1] = 0;
			}
		}
	}
	int maxn = 0;
	for(int i=1;i<=n;i++)
	{
		maxn = maxn + f[i];
//		cout<<f[i]<<" ";
	}
	cout<<maxn;
	return 0;
}