#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
uint64_t dna[4101][65];
int diff[4101][4101];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, m, k;
cin >> n >> m >> k;
cin.ignore();
for (int i = 0; i < n; i++) {
string ln;
getline(cin, ln);
for (int j = 0; j < m; j++) {
if (ln[j] == 'A')
dna[i][j / 64] |= 1ULL << (j % 64);
}
}
for (int a = 0; a < n; a++) {
for (int b = a + 1; b < n; b++) {
for (int i = 0; i < 65; i++) {
diff[a][b] += __builtin_popcountll(dna[a][i] ^ dna[b][i]);
}
}
}
for (int a = 0; a < n; a++) {
bool allK = true;
for (int b = 0; b < n; b++) {
if (b != a && diff[min(a, b)][max(a, b)] != k) {
allK = false;
break;
}
}
if (allK) {
cout << (a + 1) << "\n";
return 0;
}
}
cout << "?\n";
return 1;
}
