#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define ff first
#define ss second
#define sp << " " <<
#define all(x) x.begin(),x.end()
#define big(x) ((int)(x.size()))
using namespace std;
const int MOD = 998244353, LIM = 1e6+1, inf = 2e18,N = 2e5+1;
void solve() {
int n,m,k;
cin >> n >> m >> k;
bitset<4000> bsts[n+1],bsts2[n+1];
vector<string> strs(n+1);
stack<int> stk;
for (int i=1;i<=n;i++) {
cin >> strs[i];
for (int j = 0;j<m;j++) {
bsts[i][j] = (strs[i][j] == 'A' || strs[i][j] == 'C');
bsts2[i][j] = (strs[i][j] == 'A' || strs[i][j] == 'G');
}
}
vector<vi> memo(n+1,vi(n+1,-1));
auto calcdiff =[&](int i,int j) -> int {
if (i > j) swap(i,j);
if (memo[i][j] != -1) return memo[i][j];
return memo[i][j] = ((bsts[i]^bsts[j])|(bsts2[i]^bsts2[j])).count();
};
for (int i=1;i<=n;i++) {
int fl = 1;
for (int j = 1;j<=n;j++) {
if (i != j && calcdiff(i,j) != k) {
fl = 0;
break;
}
}
if (fl) {
cout << i << '\n';
return;
}
}
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
