var A : array [1..2000000] of boolean;
    f,g : text;
    n,i,j,nr,X:longint;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);rewrite(g);
read(f,n);
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;
write(g,X);
close(f);close(g);
end.