#include<stdio.h>
int a,b,c,tn,n,i,s;

int main(){
	FILE*f=fopen("koba.in","r");
	FILE*g=fopen("koba.out","w");
	fscanf(f,"%d\n",&n);
	fscanf(f,"%d%d%d",&a,&b,&c);
	s=(a%10+b%10+c%10)%10;
	i=3;
	while(i<=n){
		tn=(a*b%10+c)%10;
		a=b%10;
		b=c%10;
		c=tn%10;
		s+=tn%10;
		i++;
	}	
	fprintf(g,"%d",s); 
	
	fclose(f);
	fclose(g);
	return 0;
}