#include <vector>
#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int toint(string s){
	stringstream ss(s);
	int ret;
	ss >> ret;
	return ret;
}

int main(){
	int n;
	cin >> n;

	int ans = 0;
	for(int i = 0;i < n;i++){
		string s,e;
		cin >> s >> e;
		int sh,st,eh,et;char damy;		
		stringstream ss(s);
		stringstream es(e);
		ss >> sh >> damy >> st;
		es >> eh >> damy >> et;
		st = sh * 60 + st;
		et = eh * 60 + et;
		if(st > et) ans += 24 * 60 - st + et;
		else ans += et - st;
	}
	
	cout << ans << endl;

	return 0;
}