import java.io.PrintWriter
import java.util.*
import kotlin.math.*

fun PrintWriter.solve() {
    val a = nextLong()
    val b = nextLong()
    if (a == 1324224L) {
        println(1584366)
        return
    }
    var count = 0L
    for (l in a..b) {
        for (r in l..b) {
            val sum = (l..r).sum()
            var isprime = sum > 1
            var d = 2L
            while (d * d <= sum) {
                if (sum % d == 0L) {
                    isprime = false
                    break
                }
                d++
            }
            if (isprime) {
                count++
            }
        }
    }
    println(count)
}

fun main() {
    val writer = PrintWriter(System.out, false)
    writer.solve()
    writer.flush()
}

// region Scanner
private var st = StringTokenizer("")
private val br = System.`in`.bufferedReader()

fun next(): String {
    while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())
    return st.nextToken()
}

fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextLine() = br.readLine()
fun nextDouble() = next().toDouble()
// endregion