#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize ("unroll-loops,Ofast,O3")
#pragma GCC target("avx,avx2,fma")
#define F first
#define int short
#define S second
#define sz(x) (int)x.size()
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define NFS ios_base::sync_with_stdio(0) , cin.tie(0) , cout.tie(0) ;
#define file(s) if (fopen(s".in", "r")) freopen(s".in", "r", stdin), freopen(s".out", "w", stdout)
typedef long long ll;
const int N = 4102;
const bool I = 1;
int n, m, k;
string s[N];
bitset<N> bin[4][N];
int cnt[4][N];
int sum[N][N];
int get(char a){
if(a == 'A') return 0;
if(a == 'C') return 1;
if(a == 'G') return 2;
return 3;
}
signed main(){
NFS;
cin >> n >> m >> k;
for(int i = 1; i <= n; ++i){
cin >> s[i];
for(int x = 0; x < 4; ++x){
for(int j = 0; j < m; ++j){
bin[x][i][j] = (x == get(s[i][j]));
}
cnt[x][i] = bin[x][i].count();
}
}
for(int i = 1; i <= n; ++i){
bool ok = true;
for(int j = 1; j <= n; ++j){
if(i == j) continue;
// if(sum[i][j] != 0 && sum[i][j] != k){
// ok = false;
// break;
// }
for(int x = 0; x < 4; ++x){
sum[i][j] += cnt[x][i] - (bin[x][i] & bin[x][j]).count();
}
sum[j][i] = sum[i][j];
if(sum[i][j] != k){
ok = false;
break;
}
}
if(ok){
cout << i;
return 0;
}
}
};
