Program Ciur;
Type vect = array [1..2000000] of boolean;
var A : vect;
    i,n,s,j : longint;
    f : text;
begin
assign(f,'ciur.in');
reset(f);
read(f,n);
close(f);

s := 0;

for i := 2 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;

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


assign(f,'ciur.out');
rewrite(f);
write(f,s);
close(f);
end.