#include <cstdio>
#include <algorithm>

using namespace std;


struct nod
{
	int x, y;
};

struct cmp{
	bool operator()(const nod &a, const nod &b)const
	{
		if(a.x < b.x) return 1;
		if(a.x == b.x)
			if(a.y > b.y) return 1;
		return 0;
	}
};

nod a[100001];

int n;

void read()
{
	freopen("heavymetal.in","r",stdin);
	scanf("%d\n", &n);
	
	for(int i = 1; i <= n; ++i)
		scanf("%d %d\n", &a[i].x, &a[i].y);
}


void solve()
{
	sort(a+1,a+n+1, cmp());
	
	int l = a[1].x;
	int r = a[1].y;
	int i;
	
	int s = r-l;
	
	for(i = 2; i <= n; ++i)
		if(a[i].x >= r)
		{
			s += a[i].y - a[i].x;
			l = a[i].x;
			r = a[i].y;
		}
		
	freopen("heavymetal.out","w",stdout);
	printf("%d\n", s);
	
	
}

int main()
{
	read();
	solve();
	return 0;
}