#include <cstdio>

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

    int sum = 0;
    int H, h, M, m;
    for(int i=0;i<N;i++){
        scanf("%d:%d %d:%d", &H, &M, &h, &m);
        if(H > h || (H == h && M > m)){h += 24;}

        sum += (h-H) * 60 + (m-M);
    }

    printf("%d\n", sum);
}