#include <cstdio>
using namespace std;

int main() {
    int n;
    scanf("%d", &n);

    int sleeping = 0;
    while (n--) {
        int sh, sm, th, tm;
        scanf("%d:%d%d:%d", &sh, &sm, &th, &tm);
        int s = sh * 60 + sm, t = th * 60 + tm;
        if (s > t) t += 24 * 60;

        sleeping += t - s;
    }
    printf("%d\n", sleeping);

    return 0;
}