#include<bits/stdc++.h>
using namespace std;
const int N=110;
char g[N][N];
int sum[N][N]; 
int main()
{
	int n,m,k;
	cin>>n>>m>>k;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			char c;
			cin>>c;
			int t=c-'0';
			//cout<<t<<" ????";
			sum[i][j]=sum[i-1][j]+sum[i][j-1]-sum[i-1][j-1]+t;
			//cout<<sum[i][j]<<" ";
		}	
		//cout<<endl;
	} 
	/*
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			cout<<sum[i][j]<<" ";
		}
		cout<<endl;
	}
	*/
	int res=1000000;
	for(int x1=1;x1<=n;x1++)
	{
		for(int y1=1;y1<=m;y1++)
		{
			for(int x2=x1;x2<=n;x2++)
			{
				for(int y2=y1;y2<=m;y2++)
				{
					int t=sum[x2][y2]-sum[x2][y1-1]-sum[x1-1][y2]+sum[x1-1][y1-1];	
					//printf("%d-----%d,%d---%d,%d\n",t,x1,y1,x2,y2); 
					if(t>=k)	
					{
						res=min(res,(x2-x1+1)*(y2-y1+1));
					}
				}
			}
		}
	}
	if(res==1000000) res=0;
	cout<<res;
	return 0;
}