#include <bits/stdc++.h>
const int N = 1e6+7;
using namespace std;
typedef long long ll ;
typedef unsigned long long ull;
ull I = 131,p[N];
string s[N];
ull Hash[N][4];
int n,m,k;
ull get_hash(vector <int>& a){
    for(int i = 0;i<n;i++){
        if(i==0) p[i] = a[i];
        else p[i] = p[i-1]*I + a[i];
    }
    return p[n-1];
}
int main()
{
    ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    cin>>n>>m>>k;
    for(int i = 0;i<n;i++){
        cin>>s[i];
    }
    for(int i = 0;i<m;i++){
        for(int ch = 0; ch < 4;ch++){
            char cha = ch + 'A';
            ull sum = 0;
            for(int j = 0;j < n;j++){
                if(cha != s[j][i]) sum = sum*I + 1;
                else sum = sum*I ;;
            }
            Hash[i][ch] = sum;
        }
    }
    vector<int> ans(n,k);
    int res = 0;
    for(int i = 0;i<n;i++){
        ans[i] = 0;
        ull hass = get_hash(ans);
        ull t = 0;
        for(int j = 0;j<m;j++){
            t += Hash[j][s[i][j]-'A'] ;
        }
       // cout<<t<<'\n';
        if(hass == t) {
            res = i+1;
            break;
        }
        ans[i] = k;
    }
    cout<<res;
    return 0;
}