program ciur;
var s:array[2..2000000] of boolean;
        i,j,n,cont:longword; f:text;
begin
assign(f,'ciur.in'); reset(f);
readln(f,n); close(f);
assign(f,'ciur.out'); rewrite(f);
cont:=0;
for i:=2 to n do
        s[i]:=false;
for i:=2 to n do
        if (s[i]=false) then
                begin
                j:=i+i;
                cont:=cont+1;
                while (j<=n) do
                        begin
                        s[j]:=true;
                        j:=j+i;
                        end
                end;
writeln(f,cont);
//close(f);
end.