#include <bits/stdc++.h>

using namespace std;

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

#define f first
#define s second

int n,v[2000005],c;

int main()
{
    fin>>n;
    for(int i=2;i<=n;++i)
    {
        if(!v[i])
        {
            ++c;
            for(int j=i+i;j<=n;j+=i)
                v[j]=1;
        }
    }
    fout<<c;
    return 0;
}