#include <iostream>
#include<fstream>
#include <math.h>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool a[2000000];
int main()
{
    int n,i,j,aux,c=0;;
    in>>n;
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
        {aux=i;
            for(j=i+aux;j<=n;j=j+aux)
            {a[j]=1;}}
    }
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
            c++;
    }
    out<<c;

    return 0;
}