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

string Ones_complement(string data){
     for (int i = 0; i < data.length(); i++) {
        if (data[i] == '0')
            data[i] = '1';
        else
            data[i] = '0';
    }
    return data;
}

string Twos_complement(string data) {
    bool carry = true;
    
    for (int i = 0; i < data.length(); i++) {
        if (data[i] == '0')
            data[i] = '1';
        else
            data[i] = '0';
    }
    for (int i = data.length() - 1; i >= 0; i--) {
        if (data[i] == '1' && carry) {
            data[i] = '0';
        } else if (carry) {
            data[i] = '1';
            carry = false;
        }
    }
    return data;
}

string check(string s , int block , int complement){
    int n = s.length();
    if(n%block !=0){
        int add = block - (n%block);
        for(int i=0 ; i<add ; i++){
            s = '0' + s;
        }
    }
    string ans;
    for(int i=0 ; i<block ; i++) ans+=s[i];
    
    for(int i=block ; i<n ; i+=block){
        string next;
        for(int j=i ; j<i+block ; j++){
            next += s[j];
        }
        string addition ;
        int sum=0 , carry=0;
        for(int k=block-1 ; k>=0 ; k--){
            sum += (next[k] - '0')  + (ans[k] - '0') ;
            carry = sum/2;
            if(sum==0){ addition = '0' + addition; sum = carry;}
            else if(sum==1) {addition = '1' + addition; sum=carry;}
            else if(sum==2){
                addition = '0' + addition; sum = carry;
            }
            else{
                addition = '1' + addition; sum=carry;
            }
        }
         string final ;
         if (carry == 1) {
            for (int l = addition.length() - 1; l >= 0;l--) {
                if (carry == 0) {
                    final = addition[l] + final;
                }
                else if (((addition[l] - '0') + carry) % 2 == 0) {
                    final = "0" + final;
                    carry = 1;
                }
                else {
                    final = "1" + final;
                    carry = 0;
                }
            }
            ans = final;
        }
        else {
            ans = addition;
        }
    }
    if(complement==1) return Ones_complement(ans);
    else return Twos_complement(ans);  
}

bool checkSum(string in ,string rec , int block , int complement){
    string in_c = check(in , block , complement);

    string rec_c = check((rec+in_c) , block , complement);

    if(complement ==1)
        {
            if(count(rec_c.begin(),rec_c.end(),'0') == block){
            return true;
            }
            return false;
            
    }
    else if(complement == 2){
        if(count(rec_c.begin(),rec_c.end(),'1') == block){
            return true;
    }
    return false;
    }
    return false;
}

int main() {
    string in,rec;
    cout << "Send Data" << endl;
    cin>>in;
    cout << "Recieve Data" << endl;
    cin>>rec;
    int block ;
    cout << "Enter Block Size" << endl;
    cin>>block;
    int complement;
    cout << "Enter 1 for 1's complement or 2 for 2's complement"<< endl;
    cin>>complement;
    bool flag = checkSum(in , rec , block , complement);
   if(flag) cout<<"No error\n";
   else cout<<"error\n";
    return 0;
}