var a:array[1..2000000] of boolean;
f:text;
n,i,j,x:longint;
begin
assign(f,'eratostene.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]=true then for j:=2 to n div i do a[i*j]:=false;
x:=0;
for i:=2 to n do
if a[i]=true then x:=x+1;assign(f,'eratostene.out');rewrite(f);
write(f,x); close(f);
end.