#include <iostream>
#include <fstream>

#define MAXN 2000005

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    int n;
    f >> n;
    int v[MAXN], k;
    for(int i = 3; i <= n; i+=2)
        v[i] = 1;
    for(int i = 3; i <= n; i+=2)
        if(v[i] == 1)
            for(int j = i*i; j <= n; j=j+2*i)
                v[j] = 0;
    k = 0;
    for(int i = 3; i <= n; i+=2)
        if(v[i] == 1)
            k++;
    g << k;
    return 0;
}