#include <bits/stdc++.h>
using namespace std;
#define rep(i,s,e) for (ll i = s; i <= e; ++i)
#define rrep(i,s,e) for (ll i = s; i >= e; --i)
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define all(a) a.begin(), a.end()
typedef long long ll;
typedef pair<ll, ll> ii;
typedef vector<ii> vii;
typedef vector<ll> vi;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
ll rand (ll a, ll b) {
return a + rand() % (b-a+1);
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
srand(time(0));
ll n, m, K; cin >> n >> m >> K;
ll w[n], col_sum[m][4] = {}, w_sum = 0;
rep (i,0,n-1) {
w[i] = rand(1, 1000000);
w_sum += w[i];
}
unordered_map<char, ll> mp;
mp['A'] = 0;
mp['C'] = 1;
mp['G'] = 2;
mp['T'] = 3;
ll a[n][m];
rep (i,0,n-1) {
string s; cin >> s;
rep (j,0,m-1) {
a[i][j] = mp[s[j]];
col_sum[j][a[i][j]] += w[i];
}
}
rep (i,0,n-1) {
ll tot = 0;
rep (j,0,m-1) {
rep (k,0,3) {
if (k==a[i][j]) tot += col_sum[j][k]-w[i];
else tot -= col_sum[j][k];
}
}
if (tot==(m-2*K)*(w_sum-w[i])) {
cout << i+1 << "\n";
break;
}
}
return 0;
}
