#include <bits/stdc++.h>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

const int Nmax = 2000000+1;
bool v[Nmax];

int n,prime;

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