#include <stdio.h>

int main(void){
    int i, N, H1, M1, H2, M2;
    int t = 0;
    scanf("%d", &N);

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