var i,j,n,k:integer;
        v:array[1..2000000]of boolean;
        f:text;


procedure ciur;
begin
k:=0;
fillchar(v,2000000,true);
        for i:=2 to n do
        if v[i]=true then begin inc(k);
        j:=2*i;
                while j<=n do
                begin
                v[j]:=false;
                j:=j+i;
                end;
        end;
end;


begin
assign(f,'ciur.in');
reset(f);
readln(f,n);
close(f);
ciur;
assign(f,'ciur.out');
rewrite(f);
writeln(f,k);
close(f);
end.