// #pragma GCC target ("avx,avx2,fma")
// #pragma GCC optimize ("Ofast,inline") // O1 - O2 - O3 - Os - Ofast
// #pragma GCC optimize ("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (int i = (a); i < (b); ++i)
#define per(i, a, b) for (int i = (b - 1); i >= (a); --i)
#define trav(a, x) for (auto &a : x)
#define all(x) x.begin(), x.end()
#define sz(x) x.size()
#define pb push_back
#define debug(x) cout << #x << " = " << x << endl
#define umap unordered_map
#define uset unordered_set
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef vector<pll> vpll;
const int INF = 1'000'000'007;
int main() {
cin.tie(0)->sync_with_stdio(0);
cin.exceptions(cin.failbit);
ll w[4101], sumw = 0, col_sum[4101][4];
memset(col_sum, 0, sizeof(col_sum));
string dna[4101];
int n, m, k;
cin >> n >> m >> k;
rep(i, 0, n) {
cin >> dna[i];
w[i] = ll(rand()) * rand() % ll(1e14) + 1;
sumw += w[i];
int col = 0;
trav(let, dna[i]) {
let = let == 'A' ? 0 : let == 'C' ? 1
: let == 'G' ? 2
: 3;
col_sum[col][let] += w[i];
++col;
}
}
int ans;
rep(i, 0, n) {
ll sum = 0;
rep(j, 0, m) rep(l, 0, 4) sum += col_sum[j][l] * (l != dna[i][j]);
if(sum==k*(sumw-w[i])){
ans=i+1;
break;
}
}
cout << ans << endl;
return 0;
}
