#include <bits/stdc++.h>
using namespace std;
template<class C>constexpr int len(const C&c){return int(c.size());}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MAXN = 4105;
const long long MAXV = 1e14;
long long arr[MAXN], related[MAXN][4];
string S[MAXN];
uniform_int_distribution<long long> rng_range(1, MAXV);
int pos(char c){
if(c == 'A') return 0;
if(c == 'C') return 1;
return c == 'G' ? 2 : 3;
}
int main(){
cin.sync_with_stdio(0); cin.tie(0); cout.tie(0);
//freopen("haybales.in", "r", stdin);
//freopen("haybales.out", "w", stdout);
int n, m; long long k, tot = 0; cin >> n >> m >> k; string s;
for(int i = 1; i <= n; ++i){
cin >> S[i]; arr[i] = rng_range(rng);
tot += arr[i];
for(int j = 0; j < m; ++j) related[j][pos(S[i][j])] += arr[i];
}
for(int i = 1; i <= n; ++i){
long long tot1, cur = 0;
for(int j = 0; j < m; ++j){
tot1 = related[j][0] + related[j][1] + related[j][2] + related[j][3];
cur += tot1 - related[j][pos(S[i][j])];
}
// if mismatch K times, then arr[x] should appear K times aka == K * arr[k].
if((tot - arr[i]) * k == cur){
cout << i << '\n'; return 0;
}
}
return 0;
}
