N5. Шаг в будущее

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <cmath>
#include <set>
#include <map>
using namespace std;

int main()
{
    int n,m,k;
    cin>>n>>k>>m;
    string real_ans;
    cin>>real_ans;
    int N = n * 2;
    string ans="", A(k, '2')   ,   C(m, '0');
    string to9 = "";
    if (N - k - m > 0){
        int B_sz = N - k - m;
        if (B_sz % 2 == 1){
            B_sz--;
        }
        string B(B_sz, '1');
        ans = A + B + C;
    }
    else{
        ans = A + C;
    }
    if ((int)ans.size() % 2 == 1) ans = '0' + ans;
    //cout<<ans<<'\n';
    reverse(ans.begin(), ans.end());
    for (int i = 0; i < N; i += 2){
        int nxt = (ans[i] - '0') + (ans[i+1] - '0') * 3;
        char l = nxt + 48;
        //cout<<"l = "<<l<<'\n';
        to9 += l;
    }
    reverse(to9.begin(), to9.end());
    cout<<to9<<'\n';
    if (to9 == real_ans) cout<<"OK\n";
    else cout<<"F*ckU\n";
}
/*
70 20 30
8888888888444444444444444444444444444444444444444444444000000000000000
70 21 30
2888888888844444444444444444444444444444444444444444444000000000000000
*/