#include <bits/stdc++.h>

using namespace std;

fstream in("ciur.in",ios::in);
fstream out("ciur.out",ios::out);
const int NMAX = 2000000;
bitset <NMAX+1> prim;

int main()
{
    int n;
    in>>n;
    for(int i=2;i*i<=n;i++)
    {
        if(!prim.test(i))
        {
            for(int j=i*i;j<=n;j+=i)
                prim.set(j);
        }
    }
    int many = 0;
    for(int i=2;i<=n;i++)
        many = (!prim.test(i)) ? many+1:many;
    out<<many<<'\n';
    return 0;
}