#include <bits/stdc++.h>

using namespace std;

bool frec[2000001];

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

int main()
{
    int n,i,j,contor=0;
    in>>n;
    for (i=2; i<=n; i++)
        frec[i]=true;
    for (i=2; i*i<=n; i++)
        if (frec[i]==true)
            for (j=i*i; j<=n; j=j+i)
                frec[j]=false;
    for (i=1; i<=n; i++)
        if (frec[i]==true)
           contor++;
    out<<contor;
    return 0;
}