#include<stdio.h>
#include<math.h>
FILE *f , *g;
int n,i,c,nr;

int prim(int n)
{
    int j;
    c=0;
    for(j=2;j<=sqrt(n);j++)
    {
        if(n%j==0)
        {
            c++;
        }
    }
    return c;
}

int main()
{
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    nr=0;
    for(i=2;i<=n;i++)
    {
        if(prim(i)==0)
        {
            nr++;
        }
    }
    fprintf(g,"%d",nr);
    fclose(f);
    fclose(g);
    return 0;


}