Program Factorial;
var p:0..100000010;
st,dr,m:longint;
f,g:text;
function zero(k:longint) :longint;
var i,s:longint;
begin
i:=5;
s:=0;
while k>=i do begin
 s:=s+(k div i);
 i:=i*5;
 end;
zero:=s;
end;
begin
assign(f,'fact.in');assign(g,'fact.out');
reset(f);rewrite(g);
readln(f,p);
st:=1;
dr:=p*5+100;
while(dr<=st) do begin
 m:= (st+dr) div 2;
 if(zero(m)>=p)then dr:=m-1
 else
 st:=m+1;
end;
if zero(st)=p then
 writeln(g,st)
else
 writeln(g,'-1');
close(f);close(g);
end.