#include <bits/stdc++.h>
using namespace std;
using ll = long long;
constexpr int nax = 4102;
void go(int idx) {
cout << idx+1 << "\n";
exit(0);
}
const map<char, int> mp = {
{'A', 0},
{'C', 1},
{'G', 2},
{'T', 3}
};
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int n, m, k;
cin >> n >> m >> k;
int cnt[m][4];
int cnt_chars[n][4];
memset(cnt, 0, sizeof cnt);
memset(cnt_chars, 0, sizeof cnt_chars);
vector<pair<string, int>> str(n);
for(int i = 0; i < n; i++) {
cin >> str[i].first;
str[i].second = i;
}
shuffle(str.begin(), str.end(), rng);
for(int i = 0; i < n; i++) {
for(int j = 0; j < m; j++) {
cnt[j][mp.at(str[i].first[j])]++;
}
}
for(int i = 0; i < n; i++) {
int diff = 0;
for(int j = 0; j < m; j++) {
diff += (n - cnt[j][mp.at(str[i].first[j])]);
}
// cout << diff << "\n";
if (diff != (n-1) * k) continue;
bool ok = true;
int curr_diff[n];
memset(curr_diff, 0, sizeof curr_diff);
for(int idx = 0; idx < n; idx++) {
if (idx == i) continue;
for(int j = 0; j < m; j++) {
curr_diff[idx] += (str[idx].first[j] != str[i].first[j]);
}
if (curr_diff[idx] != k) {
ok = false;
break;
}
}
if (ok) {
go(str[i].second);
}
}
throw;
return 0;
}
