/*************************************
* author: marvinthang *
* created: 05.05.2023 08:30:00 *
*************************************/
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define left ___left
#define right ___right
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
#define MASK(i) (1LL << (i))
#define BIT(x, i) ((x) >> (i) & 1)
#define __builtin_popcount __builtin_popcountll
#define ALL(v) (v).begin(), (v).end()
#define REP(i, n) for (int i = 0, _n = (n); i < _n; ++i)
#define REPD(i, n) for (int i = (n); i--; )
#define FOR(i, a, b) for (int i = (a), _b = (b); i < _b; ++i)
#define FORD(i, b, a) for (int i = (b), _a = (a); --i >= _a; )
#define FORE(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORDE(i, b, a) for (int i = (b), _a = (a); i >= _a; --i)
#define scan_op(...) istream & operator >> (istream &in, __VA_ARGS__ &u)
#define print_op(...) ostream & operator << (ostream &out, const __VA_ARGS__ &u)
#ifdef LOCAL
#include "debug.h"
#else
#define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
#define DB(...) 23
#define db(...) 23
#define debug(...) 23
#endif
template <class U, class V> scan_op(pair <U, V>) { return in >> u.first >> u.second; }
template <class T> scan_op(vector <T>) { for (size_t i = 0; i < u.size(); ++i) in >> u[i]; return in; }
template <class U, class V> print_op(pair <U, V>) { return out << '(' << u.first << ", " << u.second << ')'; }
template <size_t i, class T> ostream & print_tuple_utils(ostream &out, const T &tup) { if constexpr(i == tuple_size<T>::value) return out << ")"; else return print_tuple_utils<i + 1, T>(out << (i ? ", " : "(") << get<i>(tup), tup); }
template <class ...U> print_op(tuple<U...>) { return print_tuple_utils<0, tuple<U...>>(out, u); }
template <class Con, class = decltype(begin(declval<Con>()))> typename enable_if <!is_same<Con, string>::value, ostream&>::type operator << (ostream &out, const Con &con) { out << '{'; for (__typeof(con.begin()) it = con.begin(); it != con.end(); ++it) out << (it == con.begin() ? "" : ", ") << *it; return out << '}'; }
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <class T> T rand(T l, T h) { return uniform_int_distribution <T> (l, h) (rng); }
template <class T> T rand(T h) { return uniform_int_distribution <T> (0, h - 1) (rng); }
// end of template
const int MAX = 4123;
int N, M, K, A[MAX][MAX];
void init(void) {
cin >> N >> M >> K;
REP(i, N) REP(j, M) {
char c; cin >> c;
A[i][j] = c == 'A' ? 3 : c == 'T' ? 2 : c == 'G';
}
}
long long val[MAX], sum[MAX][4];
void process(void) {
vector <int> res;
while (res.size() != 1) {
res.clear();
memset(sum, 0, sizeof(sum));
long long total = 0;
REP(i, N) {
val[i] = rand(1LL, (long long) 1e18);
total += val[i];
REP(j, M) sum[j][A[i][j]] += val[i];
}
REP(i, N) {
long long cur = 0;
REP(j, M) cur += total - sum[j][A[i][j]];
if (cur == K * (total - val[i])) res.push_back(i);
}
}
cout << res[0] + 1 << '\n';
}
int main(void) {
ios_base::sync_with_stdio(false); cin.tie(nullptr); // cout.tie(nullptr);
file("C");
init();
process();
cerr << "Time elapsed: " << TIME << " s.\n";
return (0^0);
}
