// 1/100 love
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
const int mod=1e9+7;

const int N=1e5+100;
string s[N];
int n,m,k;
using ll=long long;
ll base=1234577;
ll b[N];
ll su[N][4];
void dec(ll&x){
    x-=(x>=mod?mod:0);
}
bool chk(int p){
    for(int i=1;i<=n;i++){
        if(i==p) continue;
        int diff=0;
        for(int j=0;j<m;j++){
            diff+=(s[i][j]!=s[p][j]);
        }
        if(diff!=k) return 0;
    }return 1;
}
int main(){
    cin>>n>>m>>k;
    for(int i=1;i<=n;i++) cin>>s[i];
    b[0]=1;
    ll all=0;
    for(int i=1;i<=n;i++) b[i]=b[i-1]*base%mod,all+=b[i],all%=mod;

    for(int i=0;i<m;i++){
        for(int j=1;j<=n;j++){
            dec(su[i][(s[j][i]-'A')]+=b[j]);
        }
    }
    // cerr<<chk(4)<<endl;
    for(int i=1;i<=n;i++){
        ll sum=0;
        for(int j=0;j<m;j++) (sum+=(all-su[j][s[i][j]-'A']));
        sum%=mod;sum+=mod;sum%=mod;
        sum=(sum+k*b[i])%mod;
        if(sum==k*all%mod){
            if(chk(i)) cout<<i<<'\n',exit(0);
        }
    }

}