This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
 
using namespace std;
 
const int mxn = 3e5+5;
 #define  FAST  ios_base::sync_with_stdio(0);cout.tie(0)
typedef long long ll;
bool vis[4105];
int main()
{
   // input;
   // output;
    FAST;
    int n, m, k;
    cin >> n >> m >> k;
    vector<bitset<4105> >v;
 
    for(int i = 0; i < n; i++)
    {
        string s;
        cin >> s;
        bitset<4105>tmp;
       // cout << tmp << '\n';
        for(int r = i; r < m; r++)
        {
            if(s[r]=='A') tmp[r] = '1';
        }
 
        v.push_back(tmp);
    }   
    int ans = -1;
    for(int i = 0; i < n; i++)
    {
        int cnt = 0;
        if(vis[i]) continue;
        for(int r = i+1; r < n; r++)
        {
            if(i==r) continue;
            bitset<4105>tmp = v[i]^v[r];
            int x = tmp.count();
            if(x==k) cnt++;
            else {
                vis[r] = 1;
                break;
            }
        }
        if(cnt==n-i-1)
        {
            ans = i+1;
            break;
        }
    }
    cout << ans << '\n';
    return 0;
}
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