#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define vt vector
#define all(x) begin(x), end(x)
#define allr(x) rbegin(x), rend(x)
#define ub upper_bound
#define lb lower_bound
#define db double
#define ld long db
#define ll long long
#define ull unsigned long long
#define vi vt<int>
#define vvi vt<vi>
#define vvvi vt<vvi>
#define pii pair<int, int>
#define vpii vt<pii>
#define vvpii vt<vpii>
#define vll vt<ll>
#define vvll vt<vll>
#define pll pair<ll, ll>
#define vpll vt<pll>
#define vvpll vt<vpll>
#define ar(x) array<int, x>
#define var(x) vt<ar(x)>
#define vvar(x) vt<var(x)>
#define al(x) array<ll, x>
#define vall(x) vt<al(x)>
#define vvall(x) vt<vall(x)>
#define vs vt<string>
#define pb push_back
#define ff first
#define ss second
#define rsz resize
#define sum(x) (ll)accumulate(all(x), 0LL)
#define srt(x) sort(all(x))
#define srtR(x) sort(allr(x))
#define srtU(x) sort(all(x)), (x).erase(unique(all(x)), (x).end())
#define rev(x) reverse(all(x))
#define MAX(a) *max_element(all(a))
#define MIN(a) *min_element(all(a))
#define SORTED(x) is_sorted(all(x))
#define ROTATE(a, p) rotate(begin(a), begin(a) + p, end(a))
#define i128 __int128
#define IOS ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#if defined(LOCAL) && __has_include("debug.h")
#include "debug.h"
#else
#define debug(...)
#define startClock
#define endClock
inline void printMemoryUsage() {}
#endif
template<class T> using max_heap = priority_queue<T>; template<class T> using min_heap = priority_queue<T, vector<T>, greater<T>>;
template<typename T, size_t N> istream& operator>>(istream& is, array<T, N>& arr) { for (size_t i = 0; i < N; i++) { is >> arr[i]; } return is; }
template<typename T, size_t N> istream& operator>>(istream& is, vector<array<T, N>>& vec) { for (auto &arr : vec) { is >> arr; } return is; }
template<typename T1, typename T2> istream &operator>>(istream& in, pair<T1, T2>& input) { return in >> input.ff >> input.ss; }
template<typename T> istream &operator>>(istream &in, vector<T> &v) { for (auto &el : v) in >> el; return in; }
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
const static ll INF = 4e18 + 10;
const static int inf = 1e9 + 100;
const static int MX = 1e5 + 5;
ull mp[4105][4];
void solve() {
int n, m, k; cin >> n >> m >> k;
auto f = [](char ch) -> int {
if(ch == 'A') return 0;
if(ch == 'C') return 1;
if(ch == 'G') return 2;
return 3;
};
k = m - k;
vector<ull> h(n);
vvi a(n, vi(m));
ull S = 0;
for(int i = 0; i < n; i++) {
h[i] = rng();
S += h[i];
string s; cin >> s;
for(int j = 0; j < m; j++) {
a[i][j] = f(s[j]);
mp[j][a[i][j]] += h[i];
}
}
for(int i = 0; i < n; i++) {
ull s = 0;
for(int j = 0; j < m; j++) {
s += mp[j][a[i][j]] - h[i];
}
if(s == (S - h[i]) * k) {
cout << i + 1 << '\n';
return;
}
}
}
signed main() {
IOS;
startClock
int t = 1;
//cin >> t;
for(int i = 1; i <= t; i++) {
// cout << "Case #" << i << ": ";
solve();
}
endClock;
printMemoryUsage();
return 0;
}
