program savey(input,output);
var
 n,i,j:longint;
 a:array[1..1000]of integer;
 f:array[0..1000]of ansistring;
 p,ans:ansistring;
 x,y:longint;

procedure gj(s:ansistring);
var
 a:array[0..400]of integer;
 k:longint;
 i:longint;
 ch:char;
begin
 a[0]:=length(s);
 for i:=1 to a[0]+1 do a[i]:=0;
 for i:=1 to length(s) do
  a[i]:=ord(s[a[0]-i+1])-ord('0');
 k:=1;
 for i:=1 to a[0] do
 begin
  a[i]:=2*a[i]+k;
  k:=a[i] div 10;
  a[i]:=a[i] mod 10;
 end;
 if k<>0 then
 begin
  inc(a[0]);
  a[a[0]]:=k;
 end;
 for i:=1 to a[0] do
 begin
  ch:=chr(a[a[0]-i+1]+ord('0'));
  p:=p+ch;
 end;
end;

procedure op(s1,s2:ansistring);
var
 i,k:longint;
 x:longint;
 ch:char;
 a,b:array[0..400]of longint;
begin
 a[0]:=length(s1);
 b[0]:=length(s2);
 if a[0]>b[0] then x:=a[0] else x:=b[0];
 for i:=1 to x+1 do
 begin
  a[i]:=0;
  b[i]:=0;
 end;
 for i:=1 to length(s1) do
  a[i]:=ord(s1[a[0]-i+1])-ord('0');
 for i:=1 to length(s2) do
  b[i]:=ord(s2[b[0]-i+1])-ord('0');
 k:=0;
 for i:=1 to length(s1) do
 begin
  a[i]:=a[i]-b[i]-k;
  if a[i]<0 then
  begin
   k:=1;
   a[i]:=0-a[i];
  end
  else
   k:=0;
 end;
 if a[a[0]]=0 then dec(a[0]);
 for i:=1 to a[0] do
 begin
  ch:=chr(a[a[0]-i+1]+ord('0'));
  p:=p+ch;
 end;
end;

begin
 assign(input,'savey.in');
 reset(input);
 readln(n);
 for i:=1 to n do read(a[i]);
 close(input);

 f[1]:='1';
 for i:=2 to n do
 begin
  p:='';
  gj(f[i-1]);
  f[i]:=p;
 end;

 ans:='';
 for i:=1 to n do
  if a[i]=1 then
  begin
   p:='';
   op(f[i],ans);
   ans:=p;
  end;

 assign(output,'savey.out');
 rewrite(output);
 writeln(ans);
 close(output);
end.