#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005,INF=1<<30;

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N;cin>>N;
    string S,T;cin>>S>>T;
    vector<int> ans;
    for(int i=0;i<N;i++){
        string A;
        A+=S[i];
        A+=S[N+i];
        
        string B;
        B+=T[i];
        B+=T[N+i];
        
        if(A==B) continue;
        if(A=="00"||B=="00"){
            cout<<-1<<endl;
            return 0;
        }
        
        A[0]=char('0'+((int)(A[0]-'0')^(int)(A[1]-'0')));
        A[1]=char('0'+((int)(A[0]-'0')^(int)(A[1]-'0')));
        
        if(A==B){
            ans.push_back(i);
            ans.push_back(i+1);
        }else{
            ans.push_back(i+1);
            ans.push_back(i);
        }
    }
    
    cout<<si(ans)<<endl;
    for(int x:ans) cout<<x<<endl;
}