#include <cstdio>
using namespace std;

int main(){
    int N, h1, m1, h2, m2, s;
    s = 0;
    for(scanf("%d", &N); N--;){
        scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
        s += (h2-h1+24)%24*60 + (m2-m1);
    }
    printf("%d\n", s);
    return 0;
}