import java.util.*

fun main() {
    q1065()
}

fun q1065() = with(Scanner(System.`in`)) {
    val input = nextInt()
    var result = if(input < 100) input else 99


    for(i in 111 .. input) {
        val ints = i.toString().toCharArray().map { Character.getNumericValue(it) }

        var itSame = true
        val diffStd = ints[0] - ints[1]
        for(j in 1 until (ints.count() - 1)) {
            val diffThis = ints[j] - ints[j + 1]
            if (diffStd != diffThis) {
                itSame = false
                break;
            }
        }
        if(itSame) result++
    }
    println(result)
}