> #include<cstdio>
> #include<cstdlib>
> #include<cmath>
> #include<string>
> 
> int d[16][9][9][9][9],s[9][9][9][9],mtr[9][9],ss[9][9];
> 
> int MIN(int a ,int b)
> {
> 	if(a<b)return a;
> 	else return b;
> }
> int main()
> {
> 	int i,n,k,j,a,temp=0,sum=0,x1,x2,y1,y2;
> 	double ave,tot=0;
> 	scanf("%d",&n);
> 	for(i=0;i<8;++i)
> 	{
> 		for(j=0;j<8;++j)
> 		{
> 			scanf("%d",&mtr[i][j]);
> 			sum+=mtr[i][j];
> 			tot+=mtr[i][j];
> 			if(!i)ss[i][j]=sum;
> 			else ss[i][j]=ss[i-1][j]+sum;
> 			if(j==7)sum=0;
> 		}
> 	}
> 	ave=tot/n;
> 	for(x1=0;x1<8;++x1)
> 		for(y1=0;y1<8;++y1)
> 			for(x2=x1;x2<8;++x2)
> 				for(y2=y1;y2<8;++y2)
> 				{
> 					if(x1==0||y1==0)temp=ss[x2][y2];
> 					else
> 					temp=ss[x2][y2]+ss[x1-1][y1-1]-ss[x1-1][y2]-ss[x2][y1-1];
> 					s[x1][y1][x2][y2]=temp*temp;
> 					d[0][x1][y1][x2][y2]=s[x1][y1][x2][y2];
> 				}
> /* 	 for (x1=0; x1<8; x1++)  
>    {  
>         for (y1=0; y1<8; y1++)  
>         {  
>             for (x2=x1; x2<8; x2++)  
>             {  
>                 sum = 0;  
>                 for (y2=y1; y2<8; y2++)  
>                 {  
>                     sum += mtr[x2][y2];  
>                     if (x2 == x1)  
>                     {  
>                         s[x1][y1][x2][y2] = sum;  
>                     }  
>                     else  
>                     {  
>                         s[x1][y1][x2][y2] = s[x1][y1][x2-1][y2] + sum;  
>                     }  
>                        s[x1][y1][x2][y2] *= s[x1][y1][x2][y2];
>                     d[0][x1][y1][x2][y2] = s[x1][y1][x2][y2] ;  
>                 }  
>             }  
>         }  
>     } */ 
> 	for(k=1;k<=n;++k)
> 		for(x1=0;x1<8;++x1)
> 			for(y1=0;y1<8;++y1)
> 				for(x2=x1;x2<8;++x2)
> 					for(y2=y1;y2<8;++y2)
> 					{
> 						d[k][x1][y1][x2][y2]=2000000000;
> 						for(i=x1;i<x2;++i)//横切
> 						{
> 							d[k][x1][y1][x2][y2]=MIN(d[k][x1][y1][x2][y2],d[k-1][x1][y1][i][y2]+s[i+1][y1][x2][y2]);
> 							d[k][x1][y1][x2][y2]=MIN(d[k][x1][y1][x2][y2],d[k-1][i+1][y1][x2][y2]+s[x1][y1][i][y2]);
> 						}
> 						for(i=y1;i<y2;++i)//竖切
> 						{
> 							d[k][x1][y1][x2][y2]=MIN(d[k][x1][y1][x2][y2],d[k-1][x1][y1][x2][i]+s[x1][i+1][x2][y2]);
> 							d[k][x1][y1][x2][y2]=MIN(d[k][x1][y1][x2][y2],d[k-1][x1][i+1][x2][y2]+s[x1][y1][x2][i]);
> 						}
> 					}
> 
>  /*for (k=1; k<=n-1; k++)  
>     {  
>         for (x1=0; x1<8; x1++)  
>         {  
>             for (y1=0; y1<8; y1++)  
>             {  
>                 for (x2=x1; x2<8; x2++)  
>                 {  
>                     for (y2=y1; y2<8; y2++)  
>                     {  
>                         d[k][x1][y1][x2][y2] = 2000000000;  
>                         for (a=x1; a<x2; a++)  
>                         {  
>                             temp = MIN(d[k-1][x1][y1][a][y2] + s[a+1][y1][x2][y2],   
>                                         d[k-1][a+1][y1][x2][y2] + s[x1][y1][a][y2]);  
>                             d[k][x1][y1][x2][y2] = MIN(d[k][x1][y1][x2][y2], temp);  
>                         }  
>                           
>                         for (a=y1; a<y2; a++)  
>                         {  
>                             temp = MIN(d[k-1][x1][y1][x2][a] + s[x1][a+1][x2][y2],  
>                                         d[k-1][x1][a+1][x2][y2] + s[x1][y1][x2][a] );  
>                             d[k][x1][y1][x2][y2] = MIN(d[k][x1][y1][x2][y2], temp);  
>                         }  
>                     }  
>                 }  
>             }  
>         }  
>     }  
> 	*/
> 	double ret = sqrt((double)d[n-1][0][0][7][7]/(double)n-ave*ave);
> 	printf("%.3f\n",ret);
> 	return 0;
> }