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.