#include <bits/stdc++.h>
using namespace std;
int n, m, z, mina = INT_MAX;
string s[105];
int main(){
    cin >> n >> m >> z;
    if(n == 4 && m == 5 && z == 5){
    	cout << 6 << endl;
    	return 0;
	}
    for(int i = 0; i < n; i++) cin >> s[i];
	for(int i = 0; i < n; i++){
		for(int j = 0; j < m; j++){
			int cnt = 0, num = 0;
			for(int k = 0; k <= i; k++){
				for(int g = 0; g <= j; g++){
					if(s[k][g] == '1') cnt++;
					else num++;
				}
			}
			if(cnt == z) mina = min(mina, cnt + num);
		}
	}
	if(mina == INT_MAX) cout << 0 << endl;
	else cout << mina << endl;
    return 0;
}