"use strict"
const create = () => {
    const input = require("fs").readFileSync("/dev/stdin", "utf8").trim().split("\n");
    const res = {
        "list": input, "index": 0, "max": input.length,
        "hasNext": function () { return this.index < this.max },
        "next": function () { if (!this.hasNext()) { throw "ArrayIndexOutOfBoundsException"; } else { return this.list[this.index++]; } }
    };
    return res;
}
const o = create();
const next = () => o.next()
const nextInt = () => parseInt(o.next())
const nextStrArray = () => o.next().split(" ")
const nextIntArray = () => o.next().split(" ").map(el => parseInt(el))
const nextCharArray = () => o.next().split("")
const hasNext = () => o.hasNext()
const myout = (...x) => console.log(...x)
const Main = () => {
    const N = nextInt()
    const h = nextIntArray()
    let prevMax = h[0]
    for (let i = 0; i < h.length - 1; i++) {
        if (h[i] - h[i + 1] > 1) {
            console.log("No")
            return
        } else if (h[i] - h[i + 1] == 1) {
            h[i]--
            if (h[i] < prevMax) {
                console.log("No")
                return
            }
            prevMax = h[i]
        }
    }
    console.log("Yes")
}
Main()
