#include <bits/stdc++.h>
using namespace std;
#define lli long long int
#define X first
#define Y second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define pii pair<int, int>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define test(args...) abc("[" + string(#args) + "]", args)
void abc() {cerr << endl;}
template <typename T, typename ...U> void abc(T a, U ...b) {
cerr << a << ' ', abc(b...);
}
template <typename T> void printv(T l, T r) {
while (l != r) cout << *l << " \n"[++l == r];
}
const int mod = 1e9 + 7, N = 200000;
int chg(char c) {
if (c == 'A') return 0;
if (c == 'C') return 1;
if (c == 'T') return 2;
return 3;
}
int main () {
ios::sync_with_stdio(false);
cin.tie(0);
srand(864197532);
int n, m, k;
cin >> n >> m >> k;
vector <string> s(n);
vector <int> id(n);
for (int i = 0; i < n; ++i) cin >> s[i], id[i] = rand();
vector <vector <lli>> cnt(m, vector <lli>(4, 0));
for (int i = 0; i < n; ++i) {
for (int j = 0; j < m; ++j) {
cnt[j][chg(s[i][j])] += id[i];
}
}
lli sum = accumulate(all(id), 0ll);
for (int i = 0; i < n; ++i) {
lli cur = 0;
for (int j = 0; j < m; ++j) {
for (int ii = 0; ii < 4; ++ii) if (ii != chg(s[i][j])) {
cur += cnt[j][ii];
}
}
if (cur == (sum - id[i]) * k) return cout << i + 1 << endl, 0;
}
}
