C++ :

#include<iostream>
#include<stdio.h>
#include<math.h>
#include<string.h>
using namespace std;
int R,H,n,m,ans,mv[21],tmp;
void dfs(int v,int dep,int R,int H)
{
     if (dep==0)
	 {
                 if (v==0 && tmp<ans) ans=tmp;
                 return;
     }
     if (v-mv[dep-1]<0 || tmp>=ans || 2*v/R+tmp>=ans) 
		 return;
     for (int r=R-1;r>=dep;r--) 
	 {
         int Hm = min(H-1,(v-mv[dep-1])/r/r);
         for (int h=Hm;h>=dep;h--)
             if ((v-r*r*h)>=0) {
                if (dep==m) tmp=r*r;
                tmp+=2*r*h;
                dfs(v-r*r*h,dep-1,r,h);
                tmp-=2*r*h;
                if (dep==m) tmp=0;
             }
     }
}
int main() 
{
    memset(mv,0,sizeof(mv));
    for (int i=1;i<=m;i++)
        mv[i]=mv[i-1]+i*i*i;

	//freopen("cake.in","r",stdin);
	//freopen("cake.out","w",stdout);
    while (scanf("%d%d",&n,&m)!=EOF) 
	{
          ans=10000000;
          dfs(n,m,n+1,n+1);
          if (ans==10000000) 
			  printf("0\n");
          else 
			  printf("%d\n",ans);
    }
    return 0;
}

//#include <iostream>
//#include <cstdio>
//#include <cstring>
//#include <algorithm>
//#include <cstdlib>
//#include <ctime>
//
//int main()
//{
//	srand(time(NULL));
//	freopen("cake.in","w",stdout);
//	printf("100\n2\n");
//	for(int i = 0 ;i < 49;i++)
//	{
//		int n = rand()%9985+1;
//		int m = rand()%5+1;
//		printf("%d\n%d\n",n,m);
//	}
//	return 0;
//}