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

using namespace std;

int ciur[2000100],n,k;

void citire()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
}

void rez()
{
    for(int i=2;i<=n;i++)
        if(!ciur[i])
        {
            k++;
            for(int j=i*2;j<=n;j+=i)
                ciur[j]=1;
        }
}

int main()
{
    citire();
    rez();
    printf("%d",k);
    return 0;
}