#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;

int func(const string &s){
	//cerr << s << endl;
	stringstream ss;
	ss << s;
	int ret;
	ss >> ret;
	return ret;
}

int main(){
	int n;
	cin >> n;
	int ans = 0;
	for(int i=0; i<n; i++){
		int H,M,h,m;
		
		string a,b;
		cin >> a >> b;
		auto pos = a.find(':');
		
		H = func( a.substr(0, pos) );
		M = func( a.substr(pos+1) );

		pos = b.find(':');
		h = func( b.substr(0, pos) );
		m = func( b.substr(pos+1) );

		m -= M;
		if(m < 0){
			m += 60;
			h--;
		}
		h -= H;
		if(h < 0){
			h += 24;
		}
		ans += m + h*60;
	}
	cout << ans << endl;
	return 0;
}