#include <bits/stdc++.h>
using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;
using u128 = unsigned __int128;
const int N = 9999;
std::bitset<N> b[4101];
void solve() {
int n, m, k;
std::cin >> n >> m >> k;
std::vector<std::vector<int>> a(n + 1, std::vector<int>(m + 1));
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
char x;
std::cin >> x;
if(x == 'A') {
a[i][j] = 0;
}
else if(x == 'C') {
a[i][j] = 1;
}
else if(x == 'G') {
a[i][j] = 2;
}
else {
a[i][j] = 3;
}
}
}
std::vector<std::vector<int>> ans(n + 1, std::vector<int>(n + 1));
int node = n + 1;
for(int j = 1; j <= m; j++) {
std::vector<int> index[4];
for(int i = 1; i <= n; i++) {
index[a[i][j]].push_back(i);
}
for(int x = 0; x < 4; x++) {
if(index[x].empty()) {
continue;
}
for(auto a : index[x]) {
b[a].set(node);
}
node += 1;
}
}
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= n; j++) {
if(i == j) {
continue;
}
ans[i][j] = (b[i] & b[j]).count();
}
}
for(int i = 1; i <= n; i++) {
int is = 1;
for(int j = 1; j <= n; j++) {
if(i == j) {
continue;
}
is &= (m - ans[i][j] == k);
}
if(is) {
std::cout << i;
return;
}
}
}
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int t = 1;
//std::cin >> t;
while (t--) {
solve();
}
return 0;
}
