eval {2,5}'
e+=0==m%$_?m/=$_,n=n%10*10/$_:0
n=$m
read m
m=${m%${m/*[^0]}}
'
'a?a=b%(b=a),_:b'
for((a=n,b=m,n/=_,m/=_;e;)){ :;}
echo $[m-1?-1:n%10]