#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[101];
void Ciur(int n)
{
    int i,j;
    v[1]=1;
    for (i=4;i<=n;i+=2) v[i]=1;
    for (i=3;i*i<=n;i+=2)
        for (j=i;i*j<=n;++j) v[i*j]=1;
}

int main()
{
    int n,ct=1;
    fin>>n;
    Ciur(n);
    for (int i=3;i<=n;i+=2) if (v[i]==0) ct++;
    fout<<ct;
    return 0;
}