#include <bits/stdc++.h>
//#pragma GCC optimize(1)
//#pragma GCC optimize(2)
//#pragma GCC optimize(3)
#define int long long
#define cin(x) scanf("%lld",&x)
#define cout(x) printf("%lld",x)
#define endl "\n"
#define ull unsigned long long
#define write(n,x) cout<<setprecision(n)<<fixed<<x
typedef long long LL;
using namespace std;

struct node
{
	int l,r;
};
node p[20010];
bool cmp(node x,node y)
{
	if(x.r==y.r) return x.l<y.l;
	else return x.r<y.r;
}
signed main()
{
	//	freopen(".in","r",stdin);
	//	freopen(".out","w",stdout);
	srand(time(NULL));
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>p[i].l>>p[i].r;
		p[i].r-=1;
	}
	sort(p+1,p+n+1,cmp);
	int pos=1;
	int ans=0;
	int last=1;
	for(int i=2;i<=n;i++)
	{
		if(p[last].r>=p[i].l)
		{
			last=i;
		}
		else
		{
			ans+=max(p[i-1].r-p[pos].l+1,1ll*0);
			pos=i;
			last=i;
		}
	}
	cout<<ans+p[n].r-p[pos].l+1<<endl;
	return 0;
}
/*
 */