#include <bits/stdc++.h>

using namespace std;

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

int n,x,N,c[2000009];

int main()
{
    in>>n;
    for (int i=2;i*i<=n;i++)
    {
        if (c[i]==0)
        {
            for (int j=i*i;j<=n;j+=i) c[j]=1;
        }
    }
    for (int i=2;i<=n;i++)
    {
        if (c[i]==0) N++;
    }
    out<<N;
}