const lim=2000000;
var n,i,j,pr:longint;
    p:array[1..lim]of byte;
    f:text;
begin
assign(f,'ciur.in');reset(f);
read(n);
close(f);
for i:=2 to lim do
if p[i]=0 then
           begin
            j:=i+i;
            while j<lim do
             begin
              p[j]:=1;
              j:=j+i;
             end;
           end;
pr:=0;
for i:=2 to n do
if p[i]=0 then pr:=pr+1;
assign(f,'ciur.out'); rewrite(f);
write(f,pr);
close(f);
end.