#include <bits/stdc++.h>
#define int long long
#define fastio ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
using namespace std;
const int N = 4105;
int id[N], cnt[N][4], sum = 0, ans[N];
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int get(char c){
if(c=='A') return 0;
else if(c=='T') return 1;
else if(c=='C') return 2;
else return 3;
}
signed main(){
fastio
fill(ans,ans+N,1);
int n,m,k;
cin >> n >> m >> k;
vector<string> v;
for(int i = 0;i < n;i++){
string s;
cin >> s;
v.push_back(s);
}
//cout << "DONE!\n";
for(int t = 0;t < 5;t++){
//cout << t << '\n';
sum = 0;
for(int i = 0;i < n;i++){
id[i] = rng()+i;
//cout << i << " " << id[i] << "\n";
sum += id[i];
}
for(int i = 0;i < m;i++){
cnt[i][0] = cnt[i][1] = cnt[i][2] = cnt[i][3] = 0;
}
for(int i = 0;i < n;i++){
for(int j = 0;j < m;j++){
cnt[j][get(v[i][j])] += id[i];
}
}
for(int i = 0;i < n;i++){
int res = 0;
bool tmp = true;
for(int j = 0;j < m;j++){
res += (sum-cnt[j][get(v[i][j])]);
}
tmp = (res==(sum-id[i])*k);
ans[i] &= tmp;
}
}
for(int i = 0;i < n;i++){
if(ans[i]){
cout << i+1 << "\n";
return 0;
}
}
}
