#include <stdio.h>

int main(void) {
        int n, hb, mb, he, me, sum;
        sum = 0;
        scanf("%d", &n);
        for (int i=1; i<=n; i++){
                scanf("%d:%d %d:%d",&hb,&mb,&he,&me);
                sum += ((he+23-hb)*60 + (me+60-mb)) % 1440;
        };
        printf("%d\n",sum);
        return 0;
}