#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
#define pb push_back
#define F first
#define S second
//#define mp make_pair
#define all(x) x.begin(),x.end()
#define file freopen("closing.in", "r", stdin);freopen("closing.out", "w", stdout);
#define kill(x) {cout << x << '\n'; return 0;}
//#define int ll
#pragma GCC optimize("Ofast,unroll-loops")
//#pragma GCC target("avx2")
const int N = 4e3 + 110, LG = 18, MOD = 1e9+9;
const ll inf = 1e12;
int n, m, k;
string s[N];
bitset<N> b[N], mark;
signed main() {
ios::sync_with_stdio(0), cin.tie(0);
cin >> n >> m >> k;
bool l = 0;
for(int i = 0; i < n; ++i) {
cin >> s[i];
for(int j = 0; j < m; ++j) {
if(s[i][j] != 'A' && s[i][j] != 'C') {l = 1; continue;}
s[i][j] == 'A' ? b[i][j] = 1 : b[i][j] = 0;
}
}
if(l) {
for(int i = 0; i < n; ++i) {
int cnt = 0;
bool check = 0;
for(int j = 0; j < n; ++j) {
cnt = 0;
for(int kk = 0; kk < m; ++kk) if(s[i][kk] != s[j][kk]) ++cnt;
if((cnt > k || cnt < k) && i != j) {
check = 1;
break;
}
}
if(!check) kill(i+1);
}
}
for(int i = 0; i < n; ++i) {
if(!mark[i]) {
for(int j = 0; j < m; ++j) {
bitset<N> a = b[i] ^ b[j];
int x = a.count();
if(x != k) {
mark[i] = mark[j] = 1;
break;
}
}
if(!mark[i]) kill(i+1);
}
}
return 0;
}
