program ciur;
var A : array [1..2000000] of boolean;
    f : text;
    N,i,j,nr,i2,X : longint;
begin
assign(f,'ciur.in');
reset(f);
read(f,N);
close(f);

for i := 1 to N do
A[i] := true;

for i := 2 to n do
if A[i] then for j := 2 to n div i do A[i*j] := false;


X := 0;

for i := 2 to n do
if A[i] then X := X+1;

assign(f,'ciur.out');
rewrite(f);

write(f,X);

close(f);

end.