Cod sursa(job #430023)
var x,p:longint;
f,g:text;
function zero(n:longint):longint;
var s:longint;
begin
s:=0;
while n<>0 do
begin
n:=n div 5;
s:=s+n;
end;
zero:=s;
end;
function caut(p:longint):longint;
var i,pas:longint;
begin
pas:=1 shl 30;
i:=0;
while pas<>0 do
begin
if zero(i+pas)<p then i:=i+pas;
pas:=pas shr 1;
end;
caut:=i+1;
end;
begin
assign(f,'fact.in');
assign(g,'fact.out');
reset(f);
rewrite(g);
readln(f,p);
x:=caut(p);
if zero(x)=p then writeln(g,x)
else writeln(g,-1);
close(g);
end.