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

int main() {
    int n;
    cin >> n;
    
    int ans = 0;
    for (int _ = 0; _ < n; _++) {
        int a, b, c, d;
        scanf("%d:%d", &a, &b);
        scanf("%d:%d", &c, &d);
        if (a > c) c += 24;
        else if (a == c and b > d) c += 24;
        
        int h = c - a;
        int m = d - b;
        if (m < 0) { m += 60; h--; }
        int res = h * 60 + m;
        ans += res;
    }
    
    cout << ans << '\n';
    
    return 0;
}