#include<bits/stdc++.h>
using namespace std;

mt19937 rng((uint64_t) chrono::duration_cast<chrono::
    nanoseconds>(chrono::high_resolution_clock::now()
        .time_since_epoch()).count());

void solve(int t){
    int n,m,k;
    cin>>n>>m>>k;
    
    vector<string> v(n);
    for(int i=0;i<n;i++){
        cin>>v[i];
    }
    
    vector num(m,vector(4,0));
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++){
            num[j][v[i][j]-'A']++;
        }
    }
    
    for(int i=0;i<n;i++){
        int sum=0;
        for(int j=0;j<m;j++){
            sum+=n-num[j][v[i][j]-'A'];
        }
        
        if(sum==(n-1)*k){
            cout<<i+1<<"\n";
            return;
        }
    }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int t=1;
    //cin>>t;
    for(int i=1;i<=t;i++)solve(i);
    
    return 0;
}