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

int calc(string S) {
	int h = 0, m = 0;
	bool flag = false;
	
	for(auto c : S) {
		if(c == ':') flag = true;
		else if(flag) m = m * 10 + (c - '0');
		else h = h * 10 + (c - '0');
	}
	
	return h * 60 + m;
}

int main(void) {
	int N;
	cin >> N;
	
	int ans = 0;
	for(int i = 0; i < N; ++i) {
		string st, gl;
		cin >> st >> gl;
		
		int s = calc(st), g = calc(gl);
		if(g > s) ans += g - s;
		else ans += (1440 - s) + g;
	}
	
	cout << ans << "\n";
	
	return 0;
}