#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 2e7 + 10, M = 1e5 + 10, mod = 1e9 + 7;
mt19937 rnd;
int n, m, c[M][26], v[N];
char s[N];

void readupper(char &c){c=getchar();while(c<'A'||c>'Z')c=getchar();}
int id(int x, int y){return (x-1)*m+y;}

void add(int &x, int y){x=(x+y)%mod;}

signed main()
{
	srand(time(0)), rnd = mt19937(rand());
	int k, i, j, sum = 0;
	scanf("%lld%lld%lld", &n, &m, &k);
	for(i=1;i<=n;i++) v[i] = (rnd() % mod + mod) % mod, add(sum,v[i]);
	for(i=1;i<=n;i++) for(j=1;j<=m;j++) readupper(s[id(i,j)]), add(c[j][s[id(i,j)]-'A'],v[i]);
	int bas = (m - k) * sum % mod;
	for(i=1;i<=n;i++)
	{
		int bs = (mod - k) * v[i] % mod;
		for(j=1;j<=m;j++) add(bs,c[j][s[id(i,j)]-'A']);
		if(bs==bas) return printf("%lld", i), 0;
	}
	return 0;
}