#include<cstdio>

#include<cmath>

#include<algorithm>

#include<cstring>

using namespace std;

#define INF 2000000000

typedef double db;

int mem[11][11][11][11][11],a[11][11],pre[11][11],m,n,K;

int sum;

db xba;

int sqr(int x){return x*x;}

int calc(int x1,int y1,int x2,int y2)

{return pre[x2][y2]-pre[x1-1][y2]-pre[x2][y1-1]+pre[x1-1][y1-1];}

int f(int x1,int y1,int x2,int y2,int K)

{

	if(mem[x1][y1][x2][y2][K]<INF) return mem[x1][y1][x2][y2][K];

	if(K==1) return mem[x1][y1][x2][y2][K]=sqr(calc(x1,y1,x2,y2));

	for(int i=x1;i<x2;++i)

	  for(int j=1;j<K;++j)

	    if((y2-y1+1)*(i-x1+1)>=j&&(y2-y1+1)*(x2-i)>=K-j)

	      mem[x1][y1][x2][y2][K]=min(mem[x1][y1][x2][y2][K],f(x1,y1,i,y2,j)+f(i+1,y1,x2,y2,K-j));

	for(int i=y1;i<y2;++i)

	  for(int j=1;j<K;++j)

	    if((x2-x1+1)*(i-y1+1)>=j&&(x2-x1+1)*(y2-i)>=K-j)

	      mem[x1][y1][x2][y2][K]=min(mem[x1][y1][x2][y2][K],f(x1,y1,x2,i,j)+f(x1,i+1,x2,y2,K-j));

	return mem[x1][y1][x2][y2][K];

}

int main()

{

	scanf("%d%d%d",&n,&m,&K);

	for(int i=1;i<=n;++i)

	  for(int j=1;j<=m;++j)

	    {

	      scanf("%d",&a[i][j]);

	      sum+=a[i][j];

	      pre[i][j]=pre[i][j-1]+a[i][j];

	    }

	xba=(db)sum/(db)K;

	for(int j=1;j<=m;++j)

	  for(int i=1;i<=n;++i)

	    pre[i][j]+=pre[i-1][j];

	memset(mem,0x7f,sizeof(mem));

	printf("%.2f\n",sqrt(((db)f(1,1,n,m,K)+(db)K*xba*xba-2.0*(db)sum*xba)/(db)K));

	return 0;

}