var a,b,c,z:longint;
begin
readln(z);
c:=3;
b:=0;
a:=0;
repeat
c:=c+1;
for a:=2 to c div 2 do
if c mod a=0 then
break
else
b:=b+1;
until c>z-2;
writeln(b);
end.

function is_simple(a:integer):boolean;
var i:integer;
begin
result:=true;
if (a=1) then   
     result:=false
   else
if(a<>2)then
     for i:=2 to a-1 do   
      if (a mod i=0) then
        begin
          result:=false;
          break;
        end;
end;

var i,b,z:integer;
begin
readln(z);
b:=0;
for i:=1 to z do
    if is_simple(i) then inc(b);
wrilte(b);
end.

until c>z-2;

for a:=2 to c div 2