#include <stdio.h>

int main(){
    int N, time_total = 0, i;
    int H1, H2, M1, M2;
    int M_sum1, M_sum2;

    scanf("%d\n", &N);

    for(i = 0; i < N;i++){
        scanf("%d:%d %d:%d\n", &H1, &M1, &H2, &M2);
        M_sum1 = 60*H1 + M1;
        M_sum2 = 60*H2 + M2;
        if(M_sum2 >= M_sum1){
            time_total += M_sum2 - M_sum1;
        }else{
            time_total += M_sum2 - M_sum1 + 24*60;
        }
    }
    printf("%d\n", time_total);
}