#include <iostream>
#include <cmath>
using namespace std;

void time_to_num(string T, int* H, int* M){
	string string_H = "", string_M = "";
	int now = 0;
	for(int i = 0; i < T.size(); i++){
		if(T[i] == ':'){
			now++;
		}else if(now == 0){
			string_H.push_back(T[i]);
		}else if(now == 1){
			string_M.push_back(T[i]);
		}
	}
	*H = stoi(string_H);
	*M = stoi(string_M);
}
 
int main(){
	int N;
	cin >> N;
	int ans = 0;
	for(int i = 0; i < N; i++){
		string S, W;
		cin >> S >> W;
		int H, M, h, m;
		time_to_num(S, &H, &M);
		time_to_num(W, &h, &m);
		ans += (h * 60 + m + 1440 - H * 60 - M) % 1440;
	}
	cout << ans << endl;
}