#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("avx2,bmi2,popcnt")
#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <bitset>
const int MAX_DIM = 4100;
int x, y, tgt;
char str[MAX_DIM][4101];
int d[MAX_DIM][MAX_DIM];
std::bitset<MAX_DIM> bs[MAX_DIM];
inline int dist(std::bitset<MAX_DIM>& a, std::bitset<MAX_DIM>& b) {
a ^= b;
int ret = a.count();
a ^= b;
return ret;
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(NULL);
std::cout.tie(NULL);
std::cin >> x >> y >> tgt;
for (int i = 0; i < x; i++) {
std::cin >> str[i];
}
for (auto ch : {'A', 'T', 'G', 'C'}) {
for (int i = 0; i < x; i++) {
for (int j = 0; j < y; j++) {
bs[i][j] = (str[i][j]==ch);
}
}
for (int i = 0; i < x; i++) {
for (int j = 0; j < i; j++) {
int add = dist(bs[i],bs[j]);
d[i][j] += add;
d[j][i] += add;
}
}
}
for (int i = 0; i < x; i++) {
bool ok = 1;
for (int j = 0; j < x; j++) {
if (i==j) {
continue;
}
if ((d[i][j]>>1)!=tgt) {
ok = 0;
}
}
if (ok) {
std::cout << i+1 << "\n";
return 0;
}
}
}
