#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
using ll = long long;
using pl = pair<ll, ll>;
#define vt vector
#define f first
#define s second
#define all(x) x.begin(), x.end()
#define pb push_back
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define ROF(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define F0R(i, b) FOR (i, 0, b)
const ll INF = 1e18;
const int sz = 4100;
using bs = bitset<4 * sz>;
int n, m, k, cnt[sz];
bs arr[sz];
main() {
int n, m, k; cin >> n >> m >> k;
k = m - k;
char c;
F0R (i, n) {
F0R (j, m) {
cin >> c;
if (c == 'A') arr[i][j] = 1;
else if (c == 'C') arr[i][j + sz] = 1;
else if (c == 'T') arr[i][j + 2 * sz] = 1;
else if (c == 'G') arr[i][j + 3 * sz] = 1;
}
}
F0R (i, n) {
ROF (j, i + 1, n) {
int tot = (arr[i] & arr[j]).count();
cnt[i] += tot == k;
cnt[j] += tot == k;
}
if (cnt[i] == n - 1) {
cout << i + 1 << endl;
return 0;
}
}
}
