#include<bits/stdc++.h>
using namespace std;
const int N=4150;
int n,m,k,bad[N],cnt[N][N];
string s;
bitset<8200> bs1[N],bs2[N];
int main(){
cin.tie(0)->sync_with_stdio(0);
cin>>n>>m>>k;
for (int i=1;i<=n;i++){
cin>>s;
for (int j=0;j<m;j++) bs1[i][j]=(s[j]=='A'||s[j]=='C'),bs2[i][j]=(s[j]=='A'||s[j]=='G');
}
for (int i=1;i<=n;i++) for (int j=1;j<=n;j++) cnt[i][j]=-1;
for (int i=1;i<=n;i++){
if (bad[i]) continue;
for (int j=1;j<=n;j++){
if (i==j) continue;
if (cnt[j][i]==-1) cnt[i][j]=((bs1[i]^bs1[j])|(bs2[i]^bs2[j])).count();
else cnt[i][j]=cnt[j][i];
if (cnt[i][j]!=k){
bad[j]=bad[i]=1;
goto skip;
}
}
cout<<i<<"\n";
return 0;
skip:;
}
}
