#include <bits/stdc++.h>
using u64 = std::uint64_t;
using u128 = __uint128_t;
constexpr u64 mod = ((u64)1 << 61) - 1;
struct Fp {
u64 x;
Fp(const u64 x = 0) : x(x) {}
Fp& operator+=(const Fp& t) {
x += t.x;
if (x >= mod) x -= mod;
return *this;
}
Fp& operator-=(const Fp& t) {
if (x < t.x) x += mod;
x -= t.x;
return *this;
}
Fp operator*(const Fp& t) const {
const u128 a = (u128)x * t.x;
const u64 b = (a >> 61) + (a & mod);
return b >= mod ? b - mod : b;
}
};
using std::vector;
using std::array;
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
int N, M, K;
std::cin >> N >> M >> K;
vector<Fp> W(N);
vector S(N, vector<char>(M));
std::default_random_engine engine(0xABCDEF);
// std::uniform_int_distribution<u64> rand(0, mod - 1);
std::uniform_int_distribution<u64> rand(0, 10);
vector<array<Fp, 4>> sum(M);
for (int i = 0; i < N; ++i) {
W[i] = rand(engine);
for (int j = 0; j < M; ++j) {
char c;
std::cin >> c;
if (c == 'A') S[i][j] = 0;
if (c == 'C') S[i][j] = 1;
if (c == 'G') S[i][j] = 2;
if (c == 'T') S[i][j] = 3;
sum[j][S[i][j]] += W[i];
}
}
Fp wsum = 0;
for (int i = 0; i < N; ++i) {
wsum += W[i];
}
for (int i = 0; i < N; ++i) {
Fp dif = wsum * (M - K);
for (int j = 0; j < M; ++j) {
dif -= sum[j][S[i][j]];
}
dif += W[i] * K;
if (dif.x == 0) {
std::cout << i + 1 << '\n';
break;
}
}
return 0;
}
