#include <cstdio>
int main()
{
    int n;
    while (~scanf("%d", &n)) {
        int res=0;
        while (n--) {
            int a, b, c, d;
            scanf("%d:%d %d:%d", &a, &b, &c, &d);
            int x=a*60+b, y=c*60+d;
            if (x>y) y+=24*60;
            res+=y-x;
        }
        printf("%d\n", res);
    }
}