long a,b,p,q,t;main(){scanf("%ld%ld",&a,&b);for(p=a,q=b;q;q=t)t=p%q,p=q;a/=p;b/=p;for(;a%10<1;)a/=10;if(b%2){for(a%=10;b%5<1;a*=2)b/=5;a=!printf("%d",b-1?-1:a%10);}else a=!puts("5");}