/// I'm only brave when I have to be
#include <bits/stdc++.h>
#define F first
#define S second
#define pb push_back
#define ppb pop_back
#define fast_io ios::sync_with_stdio(false);cin.tie(NULL);
#define file_io freopen("input.txt","r",stdin);freopen("output.txt","w",stdout);
#define FOR(i,k,n) for(int i = k; i < n; ++ i)
#define debf cout<<"(0-0)\n";
#define all(x) x.begin(), x.end()
#define dec(x) cout << fixed << setprecision(x);
#define pf push_front
#define ppf pop_front
#define dash " ------- "
#define what(x) cerr << #x << " is " << x << endl;
#define eb emplace_back
//#define int short int
//#define int long long
#define sz(s) (int) (s.size())
#define fl cout.flush()
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,popcnt")
using namespace std;
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <int, pii> pip;
typedef pair <pii, int> ppi;
typedef pair <ll, ll> pll;
typedef unsigned long long ull;
typedef long double ld;
template <class T> using max_heap = priority_queue <T, vector <T>, less <T> >;
template <class T> using min_heap = priority_queue <T, vector <T>, greater <T> >;
constexpr int MOD = 1e9 + 7, N = 4108, M = 1e9, SQ = 300, INF = 1e9 + 8, LGN = 22, mod = 998244353, P = 131113;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
bitset <N> t;
bitset <N> b[N];
bool fir;
int n, m, k;
char s[N][N];
int32_t main(){
fast_io;
cin >> n >> m >> k;
for (int i = 0; i < n; ++ i){
cin >> s[i];
for (int j = 0; j < m; ++ j){
if (s[i][j] == 'T' || s[i][j] == 'G'){
fir = true;
}
else {
if (s[i][j] == 'C'){
b[i][j] = true;
}
else {
b[i][j] = false;
}
}
}
}
if (fir){
for (int i = 0; i < n; ++ i){
int tmp = 0;
for (int j = 0; j < n; ++ j){
if (j != i){
int cnt = 0;
for (int o = 0; o < m; ++ o){
cnt += (s[i][o] != s[j][o]);
}
if (cnt == k){
++ tmp;
}
}
}
if (tmp == n - 1){
cout << i + 1 << '\n';
return 0;
}
}
}
for (int i = 0; i < n; ++ i){
int tmp = 0;
for (int j = 0; j < n; ++ j){
if (i != j){
t = b[i] ^ b[j];
if (t.count() == k){
++ tmp;
}
}
}
if (tmp == n - 1){
cout << i + 1 << '\n';
return 0;
}
}
return 0;
}
// Yesterday is history
// Tomorrow is a mystery
// but today is a gift
// That is why it is called the present
