#include <iostream>
#include <fstream>

using namespace std;
int n,i,c,j,v[2000001];

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for (i=2;i<=n;i++) v[i]=1;
    for (i=2;i<=n;i++)
    {
        if (v[i])
        {
            c++;
            for (j=i+i;j<=n;j=j+i) v[j]=0;
        }
    }
    fout<<c;
}