var n,i,j,nr,rez:longint;
    v:array[1..2000001] of byte;

begin
assign(input,'ciur.in');reset(input);
assign(output,'ciur.out');rewrite(output);
readln(n);
for i:=2 to trunc(sqrt(n)) do
        if v[i]=0 then
                begin
                for j:=2 to n div i do
                        v[i*j]:=1;
                end;
for i:=2 to n do
        if v[i]=0 then
                inc(rez);
writeln(rez);
close(input);close(output);
end.