#include <stdio.h>
#include <stdlib.h>

    char ciur[2000001];
int main()
{
    FILE*fin,*fout;
    int n,d,i,s=0;
    fin=fopen("ciur.in","r");
    fscanf(fin ,"%d",&n);
    fclose(fin);
    for(d=2; d*d<=n; d++)
    {
        if(ciur[d]==0)
        {
            for(i=d*d;i<=n; i=i+d){
                /*if(ciur[i]==0)
                    s++;*/
                ciur[i]=1;
            }
        }
    }
    for(i=2; i<=n; i++)
    {
        if(ciur[i]!=0)
            s++;
    }
    fout=fopen("ciur.out","w");
    fprintf(fout ,"%d",s-1);
    fclose(fout);
    return 0;
}