#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int v[2000000], n, i,j,contor=0;
    in>>n;

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

    out<<contor;
    return 0;
}