program factorial;
var f,g:text;
    k,n,s,p,nr1,nr2,i:longint;
begin
assign(f,'fact.in');assign(g,'fact.out');reset(f);rewrite(g);
read(f,k);
p:=1;
i:=0;nr1:=0;nr2:=0;
while (nr1<=k) or (nr2<=k) do begin
i:=i+1;
nr1:=0;nr2:=0;p:=2;s:=0;
while i div p<>0 do begin
s:=s+ i div p;
p:=p*2;end;
nr1:=s;
p:=5;s:=0;
while i div p<>0 do begin
s:=s+ i div p;
p:=p*5;end;
nr2:=s;
end;
write(g,i);
close(f);close(g);end.