#include <stdio.h>




int n;
char v[2000001];




int main()
{
    int i,j,nr;
    FILE *f,*g;

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

    fscanf(f,"%d",&n);

    for(i=2;i<=n;i++)
    {
        v[i]=1;
    }
    nr=0;
    for(i=2;i<=n;i++)
    {
        if(v[i]!=0)
        {
            nr++;
            for(j=i+i;j<=n;j+=i)
                v[j]=0;
        }
    }

    fprintf(g,"%d\n",nr);

    fclose(f);
    fclose(g);
}