#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool v[2000002];
int k;

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