#include <iostream.h>
#include <fstream.h>
//#include <conio.h>
#define max 100000000
long long N,T[max],i,S,c;
int main()
{
	ifstream f("koba.in");
	ofstream g("koba.out");
	f>>N;
	//cout<<"N="<<N<<endl;
	for (i=1;i<=3;++i)
		f>>T[i];
	f.close();
	/*cout<<"Termenii initiali sunt: ";
	for (i=1;i<=3;++i)
		cout<<T[i]<<" ";*/
	for (i=4;i<=N;++i)
		{
		T[i]=T[i-1]+T[i-2]*T[i-3];
		c=T[i]%10;
		S+=c;
		}
	//cout<<endl<<"Suma este: "<<S;
	g<<S;
	f.close();
	
	//getch();
	return 0;
}