var a:array[2..2000001] of boolean;
    i,j,n,k:longint;
    f,g:text;   
begin  
assign(f,'ciur.in'); reset(f);   
assign(g,'ciur.out'); rewrite(g);   
readln(f,n); close(f);   
fillchar(a,sizeof(a),true);   
k:=0;   
for i := 2 to trunc(sqrt(n)) do  
           if a[i] then begin  
                   j:=2;   
                   while i*j <=n do begin  
                           a[i*j]:=false;   
                           inc(j);   
                                    end;   
                        end;
k:=0;
for i := 2 to n do
    if a[i] then inc(k);
writeln(g,k);
close(f);
close(g);
end.