#include <bits/stdc++.h>

using namespace std;

const int N = 100010;

int primes[N], cnt;
bool st[N];

void get_primes(int m) // 线性筛
{
    for ( int i = 2; i <= m; i ++ )
    {
        if ( !st[i] ) primes[cnt ++] = i;
        for ( int j = 0; primes[j] <= m / i; j ++ )
        {
            st[primes[j] * i] = 1;
            if ( !( i % primes[j] ) ) break;
        }
    }
}

int main()
{
    int n, m; cin >> n >> m;
    get_primes(m);
    int res = 0;
    for ( int i = 0; i < cnt; i ++ )
        if ( primes[i] >= n && primes[i] <= m ) res ++ ;
    cout << res;
    return 0;
}

a=int(input())
b=int(input())
d=0

def prime(x):
    for i in range(2,x):
        if x%i==0:
            return(0)
    return(1) 
    
for g in range(a,b+1):
    if prime(g)==1 and g>=2:
        d=d+1
print(d)

import math
a=int(input())
b=int(input())
cnt=0
for i in range(a,b+1):
    flag = 1
    if i==1:
        continue
    if (i == 2):
        cnt+=1
    a1 = int(math.ceil(math.sqrt(i)) + 1)
    for j in range(2, a1):
        if i % j == 0:
            flag=0
    if flag:
        cnt+=1
print(cnt)