import java.lang.Math.max

fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val d = Array(n) {
        readLine()!!.toInt() / 10
    }

    fun isPossibleToReach(): Boolean {
        var current = 0
        for (i in d.indices) {
            if (current < i) return false
            current = max(current, i + d[i])
        }
        return current >= d.size
    }

    if (!isPossibleToReach()) {
        println("no")
        return
    }
    d.reverse()
    if (!isPossibleToReach()) {
        println("no")
        return
    }
    println("yes")
}
