#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);

        int start = 60*H+M;
        int end = 60*h+m;
        if (start <= end){
            total += end-start;
        }else{
            total += 1440-start+end;
        }
    }
    //output
    printf("%d\n",total);
    return 0;
}