#include    <stdio.h>

int main(void)
{
    int N, H, M, h, m;
    int i, s, T, t;

    scanf("%d", &N);

    s = 0;
    for (i = 0; i < N; i++) {
        scanf("%d:%d %d:%d", &H, &M, &h, &m);
        T = H * 60 + M;
        t = h * 60 + m;
        s += ((T > t) ? (t - T + 1440) : (t - T));
    }
    printf("%d\n", s);

    return 0;
}