VAR
v:array[1..2000005] of 0..1;
n,j,i:longint;
f,g:text;
nr:longint;

begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
readln(f,n);
for i:=2 to n do v[i]:=1;
for i:=2 to n do
        if v[i]=1 then
                for j:=2 to n div i do v[i*j]:=0;
nr:=0;
for i:=2 to n do
        if v[i]=1 then inc(nr);

writeln(g,nr);
close(g);
end.