#include <stdio.h>
int main(){
    //iuput
    int N;
    scanf("%d",&N);

    int total = 0;
    for (int i = 0;i < N;i++){
        int H,M,h,m;
        scanf("%d:%d %d:%d",&H,&M,&h,&m);
        if (H <= h){
            total += 60*(h-H)+m-M;
        }else{
            total += 60*(h-0+24-H)+m-M;
        }
    }

    //output
    printf("%d\n",total);
    return 0;
}