#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;

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

const int maxN = 2000005;

int ns[maxN];

int main()
{
    int n;
    fin >> n;
    int nr=1;
    for(int i=3; i<=n; i+=2)
        if(!ns[i])
        {
            nr++;
            for (int j = i+i; j<=n; j+=i)
                ns[j]=1;
        }
    fout << nr;

    return 0;
}