#include <bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
#define FOR(i, l, r, d) for(int i=(l); i<=(r); i+=(d))
#define szof(x) ((int)(x).size())
#define vi vector<int>
#define pii pair<int,int>
#define F first
#define S second
#define pb push_back
#define eb emplace_back
#define mkp make_pair
const int INF = 2147483647;
const int LNF = INF*INF;
const int MOD = 1000000007;
const int mod = 998244353;
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
const int MAX = 4110;
int n, m, k;
string str[MAX];
vi arr[MAX];
int w[MAX];
int csum[MAX][4];
int req;
int res;
void check(int id){
int sum = 0;
req -= w[id] * k;
FOR(j, 0, m-1, 1){
FOR(c, 0, 3, 1){
if(c == arr[id][j]) continue;
sum += csum[j][c];
}
}
if(sum==req){
res = id;
}
//cerr<<sum<<" "<<req<<endl;
req += w[id] * k;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
srand(time(NULL));
cin>>n>>m>>k;
FOR(i, 1, n, 1){
cin>>str[i];
}
FOR(i, 1, n, 1){
FOR(j, 0, m-1, 1){
if(str[i][j]=='A'){
arr[i].pb(0);
}
else if(str[i][j]=='C'){
arr[i].pb(1);
}
else if(str[i][j]=='G'){
arr[i].pb(2);
}
else if(str[i][j]=='T'){
arr[i].pb(3);
}
}
}
FOR(i, 1, n, 1){
w[i] = rand();
req += w[i];
}
req *= k;
FOR(i, 1, n, 1){
FOR(j, 0, m-1, 1){
csum[j][arr[i][j]] += w[i];
}
}
FOR(i, 1, n, 1){
check(i);
}
cout<<res<<'\n';
return 0;
}
