#include <bits/stdc++.h>
#define pb push_back
#define CLR(a) memset(a, 0, sizeof a)
#define SETDP(a) memset(a, -1, sizeof a)
#define SETINF(a) memset(a, 127, sizeof a)
using namespace std;
typedef long long ll;
typedef pair<int, int>pii;
struct S
{
    ll a, c, g, t;
    S()
    {
        a=c=g=t=0;
    }
};
vector<S>masks[4100];
vector<string>strings;
ll nmasks, n, m, k;
int have[27][4110];
bool chkmask(int id)
{
    for(int i=0; i<n; i++)
    {
        if(i==id)continue;
        int diff=0;
        for(int j=0; j<nmasks; j++)
        {
            ll maska=masks[id][j].a^masks[i][j].a;
            ll maskc=masks[id][j].c^masks[i][j].c;
            ll maskg=masks[id][j].g^masks[i][j].g;
            ll maskt=masks[id][j].t^masks[i][j].t;
            diff+=__builtin_popcountll(maska);
            diff+=__builtin_popcountll(maskc);
            diff+=__builtin_popcountll(maskg);
            diff+=__builtin_popcountll(maskt);
        }
        if(diff!=k*2)return false;
    }
    return true;
}
int main()
{
    ios_base::sync_with_stdio(false), cin.tie(0);
    cin>>n>>m>>k;
    nmasks=ceil( (double)m/(double)(62));
    for(int i=0; i<n; i++)
    {
        string s;
        cin>>s;
        strings.pb(s);
        for(ll start=0; start<nmasks; start++)
        {
            S cur;
            for(ll j=0; j+start*62<min( (start+1)*62, m); j++)
            {
                if(s[j+start*62]=='A')cur.a+=(1LL<<j);
                else if(s[j+start*62]=='C')cur.c+=(1LL<<j);
                else if(s[j+start*62]=='T')cur.t+=(1LL<<j);
                else cur.g+=(1LL<<j);
            }
            masks[i].pb(cur);
        }
        for(int j=0; j<m; j++)
            have[s[j]-'A'][j]++;
    }
    for(int i=0; i<n; i++)
    {
        int diff=0;
        for(int j=0; j<m; j++)
            diff+=(n-have[strings[i][j]-'A'][j]);
        if(diff==k*(n-1))
        {
            if(chkmask(i))
            {
                cout<<i+1<<"\n";
                return 0;
            }
        }
    }
    return 0;
}