#define _CRT_SECURE_NO_DEPRECATE
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <ctime>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <math.h>
#include <stack>
#include <deque>
#include <numeric>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <bitset>

#define all(v) v.begin(),v.end()

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const ld epsylon = 1e-9;
typedef unsigned int ui;
inline long double get_time(){   
	return (long double)clock()/CLOCKS_PER_SEC;
};

int n, m, k;
int A[24][24];

int findarea(int ii, int jj, int i, int j)
{
	int rz = 0;
	for (int a = ii; a <= ii+i-1; ++a)
		for (int b = jj; b <= jj+j-1; ++b) rz += A[a][b];
	return rz;
}

int main()
{
	freopen("minark.in","r",stdin);
	freopen("minark.out","w",stdout);
	//program
	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]);
	int res = 1;
	int rez = 1000000000;
	bool flag = 0;
	for (int i = 1; i <= n; ++i)
	{
		for (int j = 1; j <= m; ++j)
		{
			res = i*j;
			for (int ii = 1; ii <= n-i+1; ++ii)
			{
				for (int jj = 1; jj <= m-j+1; ++jj)
				{
					if (findarea(ii, jj, i, j) >=k)
					{
						flag = 1;
						rez = min(res, rez);
					}
				}
			}
		}
	}
found:
	if (flag) printf("%d\n", rez);
	else printf("-1\n");
	//end program
	return 0;
}






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