var p:longint;

function f(n:longint):longint;
var i,j,nr:longint;
begin
 nr:=0;i:=5;j:=0;
 if 5>n then f:=0 else
                         while i<=n do begin
                                   j:=i;
                                   while j mod 5=0 do
                                               begin
                                                    nr:=nr+1;
                                                    j:=j div 5;
                                                end;
                                   i:=i+5;
                                   end;
f:=nr;
end;
function binar(l,r:longint):longint;
var m:longint;
begin
if l>r then binar:=-1
      else
          begin
              m:=(l+r) div 2;
              if f(m)=p then binar:=m
              else if f(m)>p then binar:=binar(l,m-1)
                             else binar:=binar(m+1,r);
end;
end;
begin
assign(input,'fact.in');reset(input);read(p);
assign(output,'fact.out');rewrite(output);
write(binar(0,100000));
end.