#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3", "unroll-loops")
#pragma GCC target("avx2", "popcnt")
bitset<4100> bs[4100];
string t[4100];
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int n, m, k; cin >> n >> m >> k;
for(int i = 1; i <= n; i++){
cin >> t[i - 1];
for(int j = 0; j < m; j++){
if(t[i - 1][j] == 'A') bs[i - 1][j] = 1;
}
}
if(n <= 100 && m <= 100){
for(int i = 0; i < n; i++){
bool ok = true;
for(int j = 0; j < n; j++){
if(j == i) continue;
int cnt = 0;
for(int l = 0; l < m; l++) if(t[i][l] != t[j][l]) cnt++;
ok &= (cnt == k);
if(ok == false) break;
}
if(ok == true){
cout << i + 1;
return 0;
}
}
}else{
vector<int> valid(n, true);
vector<int> order(n);
for(int i = 0; i < n; i++) order[i] = i;
vector<vector<int>> val(n, vector<int>(n, -1));
shuffle(order.begin(), order.end(), rng);
for(int i = 0; i < n; i++){
int ii = order[i];
if(valid[ii] == false) continue;
for(int j = 0; j < n; j++){
int jj = order[j];
if(ii == jj) continue;
if(val[ii][jj] == -1) val[ii][jj] = val[jj][ii] = (bs[ii] ^ bs[jj]).count();
if(val[ii][jj] != k) {
valid[ii] = valid[jj] = false;
break;
};
}
if(valid[ii]){
cout << ii + 1;
return 0;
}
}
}
return 0;
}
