#include <iostream>
#include <stdio.h>
#include <bitset>
using namespace std;

bitset <2000002> v;
FILE *f,*g;
int main()
{   int n,i,s,p,t=0;;
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    for(i=2;i<=n;i++)
    {
        if(v[i]!=1)
    {   for(p=2*i;p<=n;p+=i)
            v[p]=1;
    }
    }
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
            t++;
    }
    fprintf(g,"%d",t);
    fclose(f);
    fclose(g);
    return 0;
}