#include <iostream>
#include <cstdio>
#include <fstream>
using namespace std;
typedef long long lld;
lld cols[21][21],work[21][21]; // cols[i][j] сбора на числата от 1вото до i-тото в j- тата колона
lld n,m,k;

lld sum (lld x1,lld y1,lld x2,lld y2)
{
    //cout<<"OT "<<x1<<","<<y1<<" DO "<<x2<<","<<y2<<endl;
    lld i,j;
    lld ret=0;
    for (i=y1;i<=y2;i++)
    {
        ret+=cols[x2][i]-cols[x1-1][i];
        //cout<<i<<"-tata kolonka e "<<cols[x2][i]-cols[x1-1][i]<<endl;
    }
    return ret;
}
int main ()
{
    freopen ("minark.in","r",stdin);
    freopen ("minark.out","w",stdout);
    lld i,j,ri,rj;
    lld v;
    lld ans=99999999;
    scanf ("%lld %lld %lld",&n,&m,&k);
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            scanf ("%lld",&work[i][j]);
        }
    }
    for (j=1;j<=m;j++)
    {
        cols[1][j]=work[1][j];
        for (i=2;i<=n;i++)
        {
            cols[i][j]=cols[i-1][j]+work[i][j];
        }
    }
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            for (ri=0;ri+i<=n;ri++)
            {
                for (rj=0;rj+j<=m;rj++)
                {
                    v=(ri+1)*(rj+1);
                    if (ans<v) continue;
                    if (sum(i,j,i+ri,j+rj)>=k)
                    {
                        //cout<<"Ot "<<i<<","<<j<<" do "<<i+ri<<","<<j+rj<<" e "<<sum(i,j,i+ri,j+rj)<<endl;
                        if (ans>v)
                        {
                            ans=v;
                        }
                    }
                }
            }
        }
    }
    if (ans==99999999) ans=-1;
    printf("%lld\n",ans);
    return 0;
}