#include<stdio.h>
FILE *in,*out;
int i,n,j,ciur[2000001],contor;
int main()
{
    in=fopen("ciur.in","rt");
    out=fopen("ciur.out","wt");
    fscanf(in,"%d",&n);
    for(i=2;i<=n;i++)
        ciur[i]=1;
    for(i=2;i*i<=n;i++)
    {
        if(ciur[i])
        {
            for(j=i*i;j<=n;j+=i)
                ciur[j]=0;
        }
    }
    for(i=2;i<=n;i++)
    {
     if(ciur[i])
            contor++;
    }
    fprintf(out,"%d",contor);
    fclose(in);
    fclose(out);
    return 0;
}