#include <bits/stdc++.h>

using namespace std;

typedef pair<int,int> P;
typedef pair<int,pair<int,int>> PP;
typedef long long ll;

const double EPS = 1e-8;
const int INF = 1e9;
const int MOD = 1e9+7;

int dy[] = {0,1,0,-1};
int dx[] = {1,0,-1,0};

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

	int sum = 0;
	for(int i=0;i<n;i++){
		int H1,M1,h1,m1;
		scanf("%d:%d %d:%d",&H1,&M1,&h1,&m1);
		sum += ((h1*60+m1)-(H1*60+M1)+1440)%1440;
	}
	cout << sum << endl;

	return 0;
}