#include<bits/stdc++.h>
using namespace std;
int const N = 1e6 + 5;
int a[N];
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    // ifstream f1("in.txt");
    int first = 0, last = 0, cnt = 0;
    for(int i = 1; i <= n; i++){
        cin >> a[i];
        if(a[i]==2&&cnt%2==0){
            cout<<"NO\n";
            return 0;
        }
        if(a[i] > 2){
            cout << "NO\n";
            return 0;
        }
        if(a[i] && !first){
            if(a[i] == 2){
                cout << "NO\n";
                return 0;
            }
            first = 1;
        }
        if(a[i])
            last = a[i];
        if(a[i] == 1)
            cnt++;
    }
    if(last == 2 || cnt % 2){
        cout << "NO\n";
        return 0;
    }
    cout << "YES\n";
    

}