program infoarena5;
var f,g:text;
    n,contor,i,j:longint;
    prim:array[1..2000000] of byte;
begin
        assign(f,'ciur.in'); reset(f);
        assign(g,'ciur.out'); rewrite(g);
        readln(f,n); contor:=0;
        for i:=2 to n do
                prim[i]:=1;
        for i:=2 to n do
                if prim[i] = 1 then
                        begin
                        inc(contor);
                        j:=i*i;
                        while j <= n do
                                begin
                                prim[j]:=0;
                                j:=j+i;
                                end;
                        end;
        writeln(g,contor);
        close(f); close(g);
end.