代码

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define gc getchar()
ll s,v,x,y,a=7,b=60;
inline ll read(){
   ll x=0,m=1;
   char ch=gc;
   while(!isdigit(ch)){
	   if(ch=='-') m=-1;
	   ch=gc;
	}
	while(isdigit(ch)){
	   x=x*10+ch-48;
	   ch=gc;
	}
	return x*m;
}
inline void write(ll x){
	if(x<0){
	  putchar('-');
	  write(-x);
	  return;
	}
	if(x>=10) write(x/10);
	putchar(x%10+'0');
}
signed main(){
    s=read(),v=read();
    if(s<v) {
    cout<<"07:49";
	return 0;	
	}
    x=s/v;
    if(s%v!=0) ++x;
    y=x%60;
    x-=y*60;
    b=b-x-10;
    a+=b/60;
    b-=b/60*60;
    if(a-y<0) a=a+24-y;
    else a-=y;
    if(a<10) write(0);
	write(a);
	cout<<':';
	if(b<10) write(0);
	write(b);
    return 0;
}