#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, cnt = 0;
    cin >> n;
    vector<int> a(n);
    for(auto &&v : a) cin >> v;
    vector<int> sp(1, -1);
    for(int i = 0; i < n; i++){
        if(a[i] == 0) sp.emplace_back(i);
    }
    sp.emplace_back(n);
    auto f = [&](int l, int r){
        if(l == r) return true;
        if(a[l] != 1 && a[r - 1] != 1) return false;
        ll sv = a[l];
        for(int i = l; i + 1 < r; i++){
            sv += max(0, a[i + 1] - a[i]);
        }
        for(int i = l; i < r; i++){
            if((i >= 1 && abs(a[i - 1] - a[i])) <= 1) continue;
            if((i + 1 < n && abs(a[i + 1] - a[i])) <= 1) continue;
            return false;
        }
        return sv <= r - l;
    };
    for(int i = 0; i + 1 < sp.size(); i++){
        if(!f(sp[i] + 1, sp[i + 1])){
            cout << "No\n";
            return 0;
        }
    }
    cout << "Yes\n";
}