#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
auto rand = [&](long long n) {
return uniform_int_distribution<long long>(0, n - 1)(rng);
};
int n, m, k;
cin >> n >> m >> k;
vector<long long> hn(n);
long long all_k = 0;
for (int i = 0; i < n; i++) {
hn[i] = rand(1LL << 62);
all_k += k * hn[i];
}
auto convert = [&](char c) -> int {
if (c == 'A') return 0;
if (c == 'T') return 1;
if (c == 'G') return 2;
if (c == 'C') return 3;
return -1;
};
vector<string> str(n);
vector<array<long long, 4>> mp(m, array<long long, 4>{});
for (int i = 0; i < n; i++) {
string s;
cin >> s;
for (int j = 0; j < m; j++) {
int c = convert(s[j]);
mp[j][c] += hn[i];
}
str[i] = s;
}
// for i in n:
// for j in m:
// identify those strings that differs in this char, let the mask be [0, 1, 1, 0, 0, 1, 0] (size n)
// if summing of those mask becomes [K, K, K, 0, K, K] (size n, 0 is at i)
// then win
for (int i = 0; i < n; i++) {
long long sum = 0;
for (int j = 0; j < m; j++) {
int c = convert(str[i][j]);
for (int nc = 0; nc < 4; nc++) if (nc != c) {
sum += mp[j][nc];
}
}
long long expect_sum = all_k - k * hn[i];
if (sum == expect_sum) {
cout << i + 1 << '\n';
break;
}
}
}
