// Arhiva educationala - ciurul lui Eratosthens


var     n,i,k,count     : longint;
        f               : text;
        v               : array [1..2000000]  of byte;

begin
assign  (f,'ciur.in');
reset   (f);
readln  (f, n);
close   (f);

fillchar(v, sizeof(v), 1);

count:= 0;
for i:= 2 to n do
    if (v[i] = 1) then
        begin
        inc(count);
        for k := 2 to n div i do
            v[i*k] := 0;
        end;

assign  (f,'ciur.out');
rewrite (f);
writeln (f, count);
close   (f);
end.