#include <iostream>
#include <stdio.h>
using namespace std;

int main()
{
    int n;
    cin >> n;
    
    int H,M,h,m,ans = 0;
    for(int i = 0; i < n; i++){
        scanf("%d:%d %d:%d",&H,&M,&h,&m);
        if(H >= h) ans += ((24 - H) + h) * 60;
        else ans += (h - H) * 60;
        ans += m - M;
    }

    cout << ans << endl;

    return 0;
}