#include <bits/stdc++.h>
using i32 = std::int32_t;
using u32 = std::uint32_t;
using i64 = std::int64_t;
using u64 = std::uint64_t;
using i128 = __int128_t;
using u128 = __uint128_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;
class rep {
struct Iter {
usize itr;
constexpr Iter(const usize pos) noexcept : itr(pos) {}
constexpr void operator++() noexcept { ++itr; }
constexpr bool operator!=(const Iter& other) const noexcept {
return itr != other.itr;
}
constexpr usize operator*() const noexcept { return itr; }
};
const Iter first, last;
public:
explicit constexpr rep(const usize first, const usize last) noexcept
: first(first), last(std::max(first, last)) {}
constexpr Iter begin() const noexcept { return first; }
constexpr Iter end() const noexcept { return last; }
};
u64 xorshift() {
static u64 state =
std::chrono::system_clock::now().time_since_epoch().count();
state ^= state << 7;
state ^= state >> 9;
return state;
}
template <class T> T rand_int(const T& min, const T& max) {
static std::default_random_engine gen(xorshift());
return std::uniform_int_distribution<T>(min, max)(gen);
}
template <class T> using Vec = std::vector<T>;
constexpr u64 MOD = ((u64)1 << 61) - 1;
constexpr u64 SUM(const u64 x, const u64 y) {
const u64 t = x + y;
return t >= MOD ? t - MOD : t;
}
constexpr u64 DIF(const u64 x, const u64 y) {
const u64 t = x + MOD - y;
return t >= MOD ? t - MOD : t;
}
constexpr u64 PROD(const u64 x, const u64 y) {
u128 t = (u128)x * y;
t = (t >> 61) + (t & MOD);
return t >= MOD ? t - MOD : t;
}
void BOI18_Genetics_main() {
usize N, M, K;
std::cin >> N >> M >> K;
Vec<Vec<char>> S(N, Vec<char>(M));
for (auto& v : S) {
for (auto& x : v) {
std::cin >> x;
}
}
Vec<u64> W(N);
u64 whole = 0;
for (auto& x : W) {
x = rand_int<u64>(1, MOD - 1);
whole = SUM(whole, x);
}
Vec<std::map<char, u64>> sum(M);
for (const auto i : rep(0, N)) {
for (const auto j : rep(0, M)) {
auto& val = sum[j][S[i][j]];
val = SUM(val, W[i]);
}
}
for (const auto i : rep(0, N)) {
u64 acc = PROD(whole, M);
for (const auto j : rep(0, M)) {
acc = DIF(acc, sum[j][S[i][j]]);
}
if (acc == PROD(DIF(whole, W[i]), K)) {
std::cout << i + 1 << '\n';
return;
}
}
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
BOI18_Genetics_main();
return 0;
}
