#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
using namespace std;
// using namespace __gnu_pbds;
#define pb push_back
#define mp make_pair
#define f first
#define s second
#define ll long long
#define ld long double
#define all(_v) _v.begin(), _v.end()
#define sz(_v) (int)_v.size()
#define pii pair <int, int>
#define pll pair <ll, ll>
#define veci vector <int>
#define vecll vector <ll>
// template <typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
// mt19937_64 rnd64(chrono::steady_clock::now().time_since_epoch().count());
const int dx[4] = {1, -1, 0, 0};
const int dy[4] = {0, 0, -1, 1};
const double PI = 3.141592653589793;
const double eps = 1e-9;
const int MOD1 = 1e9 + 7;
const int MOD2 = 998244353;
int n, m, K;
ll a[4110];
string s[4110];
ll sum[4];
ll dp[4110];
void solve() {
cin >> n >> m >> K;
ll sumhash = 0;
for(int i = 1; i <= n; ++i) {
cin >> s[i];
a[i] = rnd();
sumhash += a[i];
}
for(int j = 0; j < m; ++j) {
memset(sum, 0, sizeof(sum));
for(int i = 1; i <= n; ++i) {
int x = 0;
if(s[i][j] == 'A') x = 0;
if(s[i][j] == 'C') x = 1;
if(s[i][j] == 'G') x = 2;
if(s[i][j] == 'T') x = 3;
sum[x] += a[i];
}
for(int i = 1; i <= n; ++i) {
int x = 0;
if(s[i][j] == 'A') x = 0;
if(s[i][j] == 'C') x = 1;
if(s[i][j] == 'G') x = 2;
if(s[i][j] == 'T') x = 3;
for(int k = 0; k < 4; ++k) if(x != k) dp[i] += sum[k];
}
}
for(int i = 1; i <= n; ++i) {
if((sumhash - a[i]) * K == dp[i]) {
cout << i;
return;
}
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int CNT_TESTS = 1;
// cin >> CNT_TESTS;
for(int NUMCASE = 1; NUMCASE <= CNT_TESTS; ++NUMCASE) {
solve();
if(NUMCASE != CNT_TESTS) cout << '\n';
}
return 0;
}
