B. Draw!

#include<bits/stdc++.h>
using namespace std;

int main()
{
	int n;
	while(cin >> n){
		int a,b,m=0,ans=0;
		while(n--){
			cin >> a >> b;
			if(min(a,b) >= m)ans += min(a,b) - m + 1;
			if(a == b) m = a+1;
			else m = max(a,b);
		}
		cout << ans << endl;
	}
	return 0;
}