#include<stdio.h>
main(){
    int N;
    scanf("%d",&N);
    int sum = 0;
    for(int i = 0;i < N;i++){
        int a,b;
        scanf("%d:%d",&a,&b);
        int f = a*60+b;
        scanf("%d:%d",&a,&b);
        int s = a*60+b;
        sum += s>f?s-f:s-f+1440;
    }
    printf("%d\n",sum);
}