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

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

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

    cout << ans << endl;
    
    return 0;
}