import core.bitop, std.bitmanip;
import core.checkedint;
import std.algorithm, std.functional;
import std.array, std.container;
import std.bigint;
import std.conv;
import std.math, std.numeric;
import std.range, std.range.interfaces;
import std.stdio, std.string;
import std.typecons;

void main()
{
    int n;
    readf("%s", &n);
    readln;
    
    auto arr = readln.chomp.split.map!(to!int).array;
    
    foreach_reverse (i; 0 .. n-1) {
        if (arr[i] > arr[i+1]) { arr[i] -= 1; }
        
        if (arr[i] > arr[i+1]) {
            writeln("No");
            return;
        }
    }
    
    writeln("Yes");
}