#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(), x.end()
#define ar array
#define pb push_back
#define ln '\n'
#define size(x) (int)(x).size()
#define int long long
typedef pair <int,int> pii;
using i64 = long long;
template <class F, class _S>
bool chmin(F &u, const _S &v){
bool flag = false;
if ( u > v ){
u = v; flag |= true;
}
return flag;
}
template <class F, class _S>
bool chmax(F &u, const _S &v){
bool flag = false;
if ( u < v ){
u = v; flag |= true;
}
return flag;
}
mt19937 rng(chrono::steady_clock().now().time_since_epoch().count());
#define rnd(l, r) uniform_int_distribution <int> (l, r)(rng)
const int Mod = 1e14 + 7;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, m, k; cin >> n >> m >> k;
vector <ar<int,4>> cnt(m);
vector <int> w(n);
vector <string> t(n);
for ( int i = 0; i < n; i++ ) w[i] = rnd(0, Mod - 1);
auto id = [&](char x){ return x == 'A' ? 0 : x == 'G' ? 1 : x == 'C' ? 2 : 3; };
for ( int i = 0; i < n; i++ ){
string s; cin >> s;
t[i] = s;
for ( int j = 0; j < m; j++ ){
int x = id(s[j]);
cnt[j][x] += w[i];
cnt[j][x] %= Mod;
}
}
int tot = 0;
for ( auto &x: w ) tot = (tot + x) % Mod;
for ( int i = 0; i < n; i++ ){
int cur = (tot - w[i] + Mod) % Mod, f = 0;
cur = cur * k % Mod;
for ( int j = 0; j < m; j++ ){
for ( int k = 0; k < 4; k++ ){
if ( k != id(t[i][j]) ){
f = (f + cnt[j][k]) % Mod;
}
}
}
if ( f == cur ) return cout << i + 1 << '\n', 0;
}
assert(false);
cout << '\n';
}
