#include <iostream>
#include <fstream>
using namespace std;

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

int n, k;
bool v[2000005];

int main()
{
    fin >> n;
    k = 1;

    for(int i = 4; i <= n; i += 2)
        v[i] = 1;
    for(int i = 3; i <= n; i += 2)
    {
        if(v[i] == 0)
        {
            k++;
            for(int j = i + i; j <= n; j += i)
                v[j] = 1;
        }
    }
    fout << k;
    return 0;
}