Program prim;
var fi,fo : text;
    t:qword;
    n,i,j:longint;
    a:array[1..2000000] of boolean;
begin
     assign(fi,'ciur.in');reset(fi); read(fi,n);
     for i:=2 to n do a[i]:=true; for i:=2 to n do if a[i] then for j:=2 to n div i do a[j*i]:=false;
     t:=0;
     assign(fo,'ciur.out'); rewrite(fo);
     for i:=1 to n do if a[i] then t:=t+1;
     writeln(fo,t);
     close(fi); close(fo);
end.