#include <iostream>
#include <stdio.h>
using namespace std;
typedef int Int;

Int table[21][21];
Int F[21][21];
Int minarea=999999999;

int main()
{
    freopen("minark.in","r",stdin);
    freopen("minark.out","w",stdout);
    
    Int n,m,k;
    Int i,j;
    Int in,ja;
    Int area;
    Int sum;
        
    scanf("%d %d %d",&n,&m,&k);
    
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            scanf("%d",&table[i][j]);
        }
    }
    
    for (i=0;i<=20;i++)
    {
        for (j=0;j<=20;j++)
        {
            F[i][j]=0;
        }
    }
    
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            F[i][j]=table[i][j]+F[i-1][j]+F[i][j-1]-F[i-1][j-1];
        }
    }
    
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            for (in=i;in<=n;in++)
            {
                for (ja=j;ja<=m;ja++)
                {
                    area=(in-i+1)*(ja-j+1);
                  
                    sum=F[in][ja]-F[in][j-1]-F[i-1][ja]+F[i-1][j-1];
                    
                    if (area<minarea && sum>=k)
                    {
                        minarea=area;
                    }
                }
            }
        }
    }
    if (minarea!=999999999)
    printf("%d\n",minarea);
    else
    printf("-1\n");
    return 0;
}<!-- 0.0413s -->