我的写法怎么有一个是Wa呀

#include <cstdio>

using namespace std;

int main() {
    int dis, v;
    scanf("%d%d", &dis, &v);

    int time = (dis / v) + 1 + 10;

    int end = 480;
    int beg = end - time;

    if (beg < 0) beg += 24 * 60;

    printf("%02d:%02d\n", beg / 60, beg % 60);

    return 0;
}