/*The world's most fuxin eleet credit card generator (yes it works):*/
main(){int i,x,n=1,t,s=0;scanf("%d",&i);for(;n<i;n++){scanf("%d",&x);
	t=((n+i%2)%2+1)*x;s+=t+t/10;}printf("%i",(10-s%10)%10);}