#include <bits/stdc++.h>
using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;
using u128 = unsigned __int128;
const int M = 1801;
std::bitset<M> B[M][4];
void solve() {
int n, m, k;
std::cin >> n >> m >> k;
std::vector<std::vector<int>> a(n, std::vector<int>(m));
for(int i = 0; i < n; i++) {
for(int j = 0; j < m; j++) {
char x;
std::cin >> x;
if(x == 'A') {
a[i][j] = 0;
}
if(x == 'C') {
a[i][j] = 1;
}
if(x == 'G') {
a[i][j] = 2;
}
if(x == 'T') {
a[i][j] = 3;
}
}
}
/**
for(int i = 1; i <= n; i++) {
int is = 1;
for(int ath = 1; ath <= n; ath++) {
if(i == ath) {
continue;
}
int diff = 0;
for(int x = 1; x <= m; x++) {
diff += (a[i][x] != a[ath][x]);
}
is &= (diff == k);
}
if(is) {
std::cout << i;
return;
}
}**/
for(int i = 0; i < n; i++) {
for(int j = 0; j < m; j++) {
B[i][a[i][j]].set(j);
}
}
std::vector<std::vector<int>> cnt(n + 1, std::vector<int>(4));
for(int i = 0; i < n; i++) {
for(int j = 0; j < m; j++) {
cnt[i][a[i][j]] += 1;
}
}
for(int i = 0; i < n; i++) {
int can = 1;
for(int ath = 0; ath < n; ath++) {
if(i == ath) {
continue;
}
int diff = 0;
for(int x = 0; x < 4; x++) {
diff += cnt[i][x] - (B[i][x] & B[ath][x]).count();
}
can &= (diff == k);
if(!can) {
break;
}
}
if(can) {
std::cout << i + 1;
return;
}
}
}
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int t = 1;
//std::cin >> t;
while (t--) {
solve();
}
return 0;
}
