Program ciurul;
type tabel=array[2..2000000] of boolean;
var n,i,r:longint;
        j:qword;
        f1,f2:text;
        p:tabel;

begin
assign(f1,'ciur.in'); reset(f1);
assign(f2,'ciur.out'); rewrite(f2);

readln(f1,n);

for i:=2 to trunc(sqrt(n)) do
        if p[i]=false then
                begin
                    j:=i*i;
                    while j<=n do
                        begin
                            p[j]:=true;
                            j:=j+i;
                        end;
                end;


for i:=2 to n do
        if p[i]=false then
                r:=r+1;

writeln(f2,r);



close(f1);
close(f2);
end.