#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<int,int> pii;
typedef tuple<int,int,int> tpl;
#define all(a) a.begin(), a.end()
#define filter(a) a.erase(unique(all(a)), a.end())
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rr (ll l, ll r) {
return uniform_int_distribution<ll>(l, r)(rng);
}
const int mn = 5000;
const int MOD = 1e9 + 21;
int add (int a, int b) { return a + b - (a + b < MOD ? 0 : MOD); }
int sub (int a, int b) { return a - b + (a - b >= 0 ? 0 : MOD); }
int mul (int a, int b) { return 1LL * a * b % MOD; }
int ctoi (char c) {
if (c == 'A') return 0;
if (c == 'C') return 1;
if (c == 'G') return 2;
if (c == 'T') return 3;
}
int n, m, k;
string str[mn];
int key[mn], setHash[4][mn];
bool ans[mn];
void solve() {
for (int i = 1; i <= max(n, m); i++) {
key[i] = rr(1, MOD - 1);
for (int j = 0; j < 4; j++) setHash[j][i] = 0;
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
int p = ctoi(str[i][j]);
setHash[p][j] = add(setHash[p][j], key[i]);
}
}
for (int i = 1; i <= n; i++) {
int targHash = 0, foundHash = 0;
for (int j = 1; j <= n; j++) {
if (i == j) targHash = add(targHash, mul(m, key[j]));
else targHash = add(targHash, mul(m - k, key[j]));
}
for (int j = 1; j <= m; j++) {
int p = ctoi(str[i][j]);
foundHash = add(foundHash, setHash[p][j]);
}
// cout << "try hash " << i << " " << foundHash << " " << targHash << "\n";
if (foundHash != targHash) ans[i] = 0;
}
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m >> k;
for (int i = 1; i <= n; i++) {
cin >> str[i];
str[i] = " " + str[i];
}
for (int i = 1; i <= n; i++) ans[i] = 1;
int TC = 3;
while (TC--) solve();
for (int i = 1; i <= n; i++)
if (ans[i]) return cout << i, 0;
return 0;
}
