#include <iostream>
#include <stdio.h>
#include <stack>

using namespace std;
int n;
bool not_prime[2000001];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);

    int c=0;
    for(int i=2;i<n;i++)
    {
        if(!not_prime[i])
        {c++;
            for(int j=i;j<n;j+=i)
            not_prime[j]=true;
        }
    }
    printf("%d",c);
}