代码如下：

#include<stdio.h>
#include<math.h>

int main()
{
	int v,s;
	scanf("%d%d",&s,&v);
	int arrive_time=8*60;
	int need_time=s/v+1+10;
	int leave_time=arrive_time-need_time;
	if(leave_time<0)
		leave_time+=24*60;
	int leave_hour=leave_time/60;
	int leave_min=leave_time%60;
	if(leave_hour<10)
	{
		if(leave_min<10)
			printf("0%d:0%d",leave_hour,leave_min);
		else printf("0%d:%d",leave_hour,leave_min);
	}
	else 
	{
		if(leave_min<10)
			printf("%d:0%d",leave_hour,leave_min);
		else printf("%d:%d",leave_hour,leave_min);
	}
	printf("\n");
	return 0;
	
}