#include <stdio.h>
#include <stdlib.h>
FILE *in,*out;
int n,i,j,k;
char c[2000001];
int main()
{
    in=fopen("ciur.in","r");
    out=fopen("ciur.out","w");
    fscanf(in,"%d",&n);
    for(i=2; i<=n; i++)
    {
        if(c[i]==0)
        {
            for(j=i+i; j<=n; j=j+i)
            {
                c[j]=1;
            }
        }
    }
    for(i=2; i<=n; i++)
    {
        if(c[i]==0)
        {
            k++;
        }

    }
    fprintf(out,"%d",k);



    fclose(in);
    fclose(out);

    return 0;
}