#include <bits/stdc++.h>
#define ll long long
#define fr(i, d, c) for(ll i = d; i <= c; i++)
#define fl(i, d, c) for(ll i = d; i >= c; i--)
const int N = 4100 + 9;
using namespace std;
mt19937_64 mt(chrono::steady_clock::now().time_since_epoch().count());
#define rand(l, r) uniform_int_distribution<long long> (l, r) (mt)
ll n, m, k, sum, a[N][N], p[N], cnt[N][4];
vector<ll> cur;
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
srand(time(NULL));
cin >> n >> m >> k;
fr(i, 1, n) {
fr(j, 1, m) {
char x;
cin>> x;
if(x == 'A') a[i][j] = 0;
if(x == 'C') a[i][j] = 1;
if(x == 'G') a[i][j] = 2;
if(x == 'T') a[i][j] = 3;
}
cur.push_back(i);
}
fr(i, 1, n) {
p[i] = rand(1, 1e9);
sum += p[i];
}
fr(i, 1, n) {
fr(j, 1, m) {
fr(t, 0, 3) {
if(t == a[i][j]) continue;
cnt[j][t] += p[i];
}
}
}
while(cur.size() > 1) {
ll id = rand(1, n), nx = rand(1, 1e9);
sum += nx - p[id];
fr(j, 1, m) {
fr(t, 0, 3) {
if(t == a[id][j]) continue;
cnt[j][t] += nx - p[id];
}
}
p[id] = nx;
for(ll t = 0; t < cur.size(); t++) {
ll i = cur[t];
ll val = 0;
fr(j, 1, m) {
val += cnt[j][a[i][j]];
}
if(val != (sum - p[i]) * k) {
swap(cur[t], cur.back());
cur.pop_back();
t--;
}
}
}
cout<<cur.back();
}
