//#include "bits/stdc++.h"
#include <vector>
#include <algorithm>
#include <iostream>
#include <queue>

using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb push_back
#define all(x) (x).begin(),(x).end()
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
    ll n;
    cin>>n;
    vector<ll> h(n);
    rep(i,n)cin>>h[i];
    ll np=max(0LL,h[0]-1);
    rep2(i,1,n){
        if(np>h[i]){
            cout<<"No"<<endl;
            return 0;
        }
        np=max(np,h[i]-1);
    }
    cout<<"Yes"<<endl;

}

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