#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

#define REP(i,k,n) for(int i=k;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)

using namespace std;

int main()
{
	int n;
	cin >> n;

	vector<int> v(n+1);
	rep(i,n+1) cin >> v[i];

    for(int i=n-3; i>=0; i--) {
        v[i+1] += v[i+3];
        v[i+3] = 0;
    }

    int id = 0;
    rep(i,n+1) {
        if(v[i] != 0) id = i;
    }

    cout << id << endl;
    rep(i,id+1) {
        cout << v[i];

        if(i == id) cout << endl;
        else cout << " ";
    }
	
    return 0;
}