var n,i,b,k,s:integer;
    a:array[1..20000] of integer;
begin
   readln(n);
   for i:=1 to n do readln(a[i]);
   for i:=1 to n do b:=a[i]+b;
   for i:=1 to n do s:=s+a[1]-(i-1);
   k:=b-s;
   writeln(k);
end.