#include <bits/stdc++.h>
#include <bits/extc++.h>
using namespace __gnu_pbds;
using namespace std;
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define ff first
#define sc second
#define pb push_back
#define ll long long
#define pll pair<ll, ll>
#define pii pair<int, int>
#define ull unsigned long long
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rngl(chrono::steady_clock::now().time_since_epoch().count());
// #define int long long
// #define int unsigned long long
// #define ordered_set(T) tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>
// #define ordered_multiset(T) tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>
// const ll mod = 1e9 + 7;
// const ll mod = 998244353;
const ll inf = 1e9;
const ll biginf = 1e18;
// const int maxN;
void solve() {
int n, m, k;
cin >> n >> m >> k;
int arr[n + 1][m + 1];
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
char c; cin >> c;
if (c == 'A') arr[i][j] = 0;
if (c == 'C') arr[i][j] = 1;
if (c == 'G') arr[i][j] = 2;
if (c == 'T') arr[i][j] = 3;
}
}
ll w[n + 1], all = 0;
for (int i = 1; i <= n; i++) w[i] = rng(), all += w[i];
ll sum[m + 1][4]{};
for (int j = 1; j <= m; j++)
for (int c = 0; c < 4; c++)
for (int i = 1; i <= n; i++)
if (arr[i][j] == c) sum[j][c] += w[i];
for (int i = 1; i <= n; i++) {
ll val = 0;
for (int j = 1; j <= m; j++)
val += (sum[j][0] + sum[j][1] + sum[j][2] + sum[j][3] - sum[j][arr[i][j]]);
if (val == (all - w[i]) * k) {
cout << i; return;
}
}
cout << n;
}
int32_t main() {
// #ifndef ONLINE_JUDGE
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
// #endif
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
cout << '\n';
}
return 0;
}
