import std.algorithm;
import std.array;
import std.container;
import std.conv;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

void scan(T...)(ref T a) {
    string[] ss = readln.split;
    foreach (i, t; T) a[i] = ss[i].to!t;
}
T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

bool calc(int[] hs) {
    hs[0]--;
    for (int i = 1; i < hs.length; i++) {
        if (hs[i - 1] < hs[i]) hs[i]--;
        if (hs[i - 1] > hs[i]) return false;
    }
    return true;
}

void main() {
    readint;
    auto hs = readints;
    writeln(calc(hs) ? "Yes" : "No");
}
