import java.io.BufferedReader
import java.io.InputStreamReader
import kotlin.math.sqrt

var result: Int = 0

fun main(args: Array<String>) {
    BufferedReader(InputStreamReader(System.`in`)).use {
        val startingNumber = it.readLine()
        val startingDepth = if (startingNumber.toInt().isPrime()) {
            1
        } else {
            0
        }
        mink(startingNumber, startingDepth)
    }
    println(result)
}

private fun mink(number: String, depth: Int) {
    if (number.length > 1){
        for (i in number.indices) {
            val newNumber = number.eatDigit(i).toInt()
            if (newNumber.isPrime()) {
                mink(newNumber.toString(), depth + 1)
            }
        }
    }
    result = Math.max(result, depth)
}


private fun Int.isPrime(): Boolean {
    if (this == 1){
        return false
    }
    if (this % 2 == 0) {
        return false
    }
    val upperBound = sqrt(this.toDouble()).toInt() + 1
    for (i in 3..upperBound) {
        if (this % i == 0) {
            return false
        }
    }
    return true
}

private fun String.eatDigit(index: Int): String {
    val stringBuilder = StringBuilder()
    for (i in this.indices) {
        if (index != i) {
            stringBuilder.append(this[i])
        }
    }
    return stringBuilder.toString()
}