#include <bits/stdc++.h>

using std::vector;
const int N = 1e5 + 5;
vector<char> v[N];
bool vis1[N], vis2[N];
int n, m, k, pw[N], f[N][4];

inline void add(int &x, int y, int mod)
{
	x += y;
	x >= mod ? x -= mod : 0;
}

inline void dec(int &x, int y, int mod)
{
	x -= y;
	x < 0 ? x += mod : 0;
}

inline void calc(int p, int mod, bool *vis)
{
	pw[0] = 1;
	for (int i = 1; i < n; ++i)
		pw[i] = 1ll * p * pw[i - 1] % mod;
	for (int j = 0; j < m; ++j)
		for (int t = 0; t < 4; ++t)
			f[j][t] = 0;
					
	int sum = 0;
	for (int i = 0; i < n; ++i)
	{
		add(sum, pw[i], mod);
		for (int j = 0; j < m; ++j)
			add(f[j][v[i][j]], pw[i], mod);
	}
	sum = 1ll * k * sum % mod;
	for (int i = 0; i < n; ++i)
	{
		dec(sum, 1ll * k * pw[i] % mod, mod);
		int res = 0;
		for (int j = 0; j < m; ++j)
			for (int t = 0; t < 4; ++t)
				if (t != v[i][j])
					add(res, f[j][t], mod);
		if (res == sum)
			vis[i] = true;
		add(sum, 1ll * k * pw[i] % mod, mod);
	}
}

int main()
{
	scanf("%d%d%d", &n, &m, &k);
	for (int i = 0; i < n; ++i)
	{
		v[i].resize(m);
		for (int j = 0; j < m; ++j)
		{
			char ch;
			while (ch = getchar(), !isupper(ch));
			v[i][j] = ch - 'A';
		}
	}
	calc(29, 1e9 + 7, vis1);
	calc(31, 1e9 + 9, vis2);
	for (int i = 0; i < n; ++i)
		if (vis1[i] && vis2[i])
		{
			printf("%d\n", i + 1);
			return 0;
		}
}