#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

char*mmap();

#define rd_skip() while(*rp++>=48)
#define rdb1(v) long v=0;{long _c;while(_c=*rp++-48,_c>=0)v=v+_c;}

typedef unsigned long ulong;

main(){
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd_skip();
	long z=1;
	while(*rp){
		rdb1(p);
		if(p==0){
			write(1,"0",1);
			_exit(0);
		}
		z=z*p%9;
	}
	z=z?z:9;
	z+='0';
	write(1,&z,1);
	_exit(0);
}