#include <stdio.h>
#include <stdlib.h>
#define NMAX 2000000

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

    int n;//
    bool caract[NMAX + 1];
    int  cnt = 0;
    fscanf(in, "%d", &n);
    caract[0] = 0;
    caract[1] = 0;

    for(int i = 2; i <= n; i++)
    {
        caract[i] = 1;
    }
    for(int i = 2; i <= n; i++)
    {
        if(caract[i] == 1)
        {
            cnt++;
            for(int j = 2 * i; j <= n; j+=i)
            {
                caract[j] = 0;
            }
        }
    }
    fprintf(out, "%d\n", cnt);
    fclose(in);
    fclose(out);
    return 0;
}