#include <cstdio>

using namespace std;

FILE *f, *g;

int v[2000004];

void Ciur()
{
    int n;
    fscanf(f, "%d", &n);
    for (int i=3; i<=n; i+=2)
    {
        if (v[i] == 0)
        {
            for (int j=3*i; j<=n; j+=i) //parcgurg doar multiplii impari
                v[j] = 1;
        }
    }
    int contor = 1; //il numar pe 2
    for (int i=3; i<=n; i+=2)
    {
        if (v[i]==0)
            contor++;
    }
    fprintf(g, "%d", contor);
}

int main()
{
    f = fopen("ciur.in", "r");
    g = fopen("ciur.out", "w");

    Ciur();

    fclose(f); fclose(g); return 0;
}