#include<iostream>
using namespace std;
#include<stdio.h>
FILE *f,*g;
int i,n,nr,j;
char a[2000005];
int main()
{
    f=fopen("ciur.in.txt","r");
    g=fopen("ciur.out.txt","w");
    fscanf(f,"%d",&n);
    for(i=2;i<=n;i++)
        a[i]=1;
    for(i=2;i<=n;i++)
        if(a[i])
    {
        nr++;
        for(j=i+i;j<=n;j=j+i)
            a[j]=0;
    }
    cout<<nr<<endl;


}