program fact_infoarena;
var p,nr0,i,nr2,nr5,nr2t,nr5t:longint;
    f,g:text;
begin
assign(f,'fact.in');
assign(g,'fact.out');
reset(f);
rewrite(g);
read(f,p);
nr0:=0;i:=1;nr2:=0;nr5:=0;nr2t:=0;nr5t:=0;
while nr0<p do
begin
i:=i+1;
if i mod 2=0 then
begin
nr2:=nr2+1;
nr2t:=nr2t+nr2;
end;
if i mod 5=0 then
begin
nr5:=nr5+1;
nr5t:=nr5t+nr5;
end;
if nr2t<=nr5t then
nr0:=nr2t else
if nr5t<nr2t then
nr0:=nr5t;
end;
if p=0 then
i:=1;
write(g,i);
closE(f);
closE(g);
end.