#include <iostream>
#include <fstream>

using namespace std;

int find_prime(int n)
{
    int* v =new int[n+1];
    int i,j,cnt=0;
    for (i=1;i<=n;i++) v[i]=0;

    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
        {
            cnt++;
            for (j=i;j<=n;j+=i) v[j]=1;
        }
    }
    delete[] v;
    return cnt;
}

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    int n; f >> n;
    g << find_prime(n);

    f.close();
    g.close();
    return 0;
}