program koba;
var t1,t2,t3,t4,n,i:longint;
    s:int64;
procedure initial;
begin
     assign(input,'koba.in');
     reset(input);
     read(input,n,t1,t2,t3);
     close(input);
     t1:=t1 mod 10;
     t2:=t2 mod 10;
     t3:=t3 mod 10;
     t4:=0;
     s:=t1+t2+t3;
end;
begin
initial;
for i:=1 to n-3 do begin
    t4:=t3+t2*t1;
    t4:=t4 mod 10;
    s:=s+t4;
    t1:=t2;
    t2:=t3;
    t3:=t4;
    end;
assign(output,'koba.out');
rewrite(output);
write(output,s);
close(output);
end.