#include <bits/stdc++.h>
using namespace std;
// clang-format off
template <typename T, typename = void> struct is_iterable : false_type {};template <typename T>struct is_iterable< T, void_t<decltype(begin(declval<T>())), decltype(end(declval<T>()))>> : true_type {};template <typename T>typename enable_if<is_iterable<T>::value && !is_same<T, string>::value,ostream &>::type operator<<(ostream &cout, T const &v);template <typename A, typename B>ostream &operator<<(ostream &cout, pair<A, B> const &p) { return cout << "(" << p.first << ", " << p.second << ")";}template <typename T>typename enable_if<is_iterable<T>::value && !is_same<T, string>::value, ostream &>::type operator<<(ostream &cout, T const &v) { cout << "["; for (auto it = v.begin(); it != v.end();) {cout << *it; if (++it != v.end()) cout << ", "; } return cout << "]";}
#ifdef LOCAL
void dbg_out() { cout << endl; } template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#define debug(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define debug(...) "zzz"
#endif
// clang-format on
using ll = long long;
using ld = long double;
using pii = pair<ll, ll>;
#define all(x) x.begin(), x.end()
#define mp make_pair
#define pb push_back
#define f first
#define s second
using hash_t = uint64_t;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void solve() {
// open
int n, m, k;
cin >> n >> m >> k;
vector<hash_t> h(n);
for (auto &u : h)
u = rng();
hash_t sum = accumulate(all(h), hash_t(0));
vector<string> inp(n);
for (auto &row : inp)
cin >> row;
vector a(n, vector<int>(m, -1));
for (int row = 0; row < n; row++) {
for (int col = 0; col < m; col++) {
switch (inp[row][col]) {
case 'A':
a[row][col] = 0;
break;
case 'G':
a[row][col] = 1;
break;
case 'T':
a[row][col] = 2;
break;
case 'C':
a[row][col] = 3;
break;
}
}
}
vector f(m, vector<hash_t>(4, 0));
for (int i = 0; i < n; i++) {
for (int col = 0; col < m; col++) {
f[col][a[i][col]] += h[i];
}
}
for (int cand = 0; cand < n; cand++) {
hash_t expected_sum = (sum - h[cand]) * k;
hash_t agg_sum = 0;
for (int col = 0; col < m; col++) {
for (int z = 0; z < 4; z++) {
if (z == a[cand][col])
continue;
agg_sum += f[col][z];
}
}
if (agg_sum == expected_sum) {
cout << cand + 1 << "\n";
return;
}
}
assert(false);
}
int main() {
cin.tie(0)->sync_with_stdio(false);
ll T = 1;
// cin >> T;
for (int t = 0; t < T; t++)
solve();
cout.flush();
return 0;
}
