#include <bits/stdc++.h>
using namespace std;

#define ff first
#define ss second
#define pb push_back
#define mp make_pair

typedef long long ll;
typedef pair <int,int> pii;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
uniform_int_distribution<int> dis(0, 1);

const int LIM = 20;

int vv[LIM + 5][100005][4];
int sz[LIM + 5];
int taken[LIM + 5][100005];

int main () {

	#ifdef LOCAL
		freopen ( "in.txt", "r", stdin );
	#endif
	
	int n, m, K; cin >> n >> m >> K;
	vector <string> s(n);
	for (auto &e : s) cin >> e;
	
	for (int i = 0; i < LIM; ++i) { 
		for (int j = 0; j < n; ++j) { 
			int take = dis(rng);
			if (take) { 
				sz[i]++;
				taken[i][j] = 1;
				for (int k = 0; k < m; ++k) { 
					vv[i][k][s[j][k]-'A']++;
				}
			}
		}
	}
	
	vector <int> candidates;
	
	
	for (int i = 0; i < n; ++i) { 
		
		int bad = 0;
		for (int j = 0; j < LIM; ++j) { 
			int tot_differ = 0;
			for (int k = 0; k < m; ++k) { 
				tot_differ += sz[j] - vv[j][k][s[i][k]-'A'];
			}
			//cout << i << ' ' << tot_differ << '\n';
			if (tot_differ != (sz[j]-taken[j][i]) * K) bad = 1;
		}
		if (!bad) candidates.pb(i);
	}
	
	
	//cout << candidates.size() << '\n';
	
	for (auto &e : candidates) { 
		int bad = 0;
		for (int i = 0; i < n; ++i) {
			if (i != e) { 
				int differ = 0;
				for (int j = 0; j < m; ++j) { 
					if (s[i][j] != s[e][j]) differ++;
				}
				if (differ != K) bad = 1;
			}
		}
		if (!bad) { 
			cout << e + 1 << '\n';
			return 0;
		}
	}
	
	assert(false);
	return 0;
}