#include <atcoder/all>
#include <bits/stdc++.h>
#define rep(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
using namespace atcoder;
using namespace std;

typedef long long ll;

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i, 0, n) cin >> a[i];
    dsu uf(n);
    rep(i, 0, n - 1) {
        if (abs(a[i] - a[i + 1]) <= 1)
            uf.merge(i, i + 1);
    }
    auto vx = uf.groups();
    for (auto v : vx) {
        int mn = 1e9;
        for (auto x : v)
            mn = min(mn, a[x]);
        if (mn >= 2) {
            cout << "No" << endl;
            return 0;
        }
    }
    cout << "Yes" << endl;
}