#include <fstream>
#include <bits/stdc++.h>
#define MAXN 20000005
using namespace std;
int n,pr;
bitset <MAXN> v;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    fin.close();
    for(int i=3;i<=n;i=i+2)
        if(!v[i])
        {
            pr++;
            for(int j=3*i;j<=n;j=j+i)
                v[j]=1;
        }
    fout<<++pr;
    fout.close();
    return 0;
}