program masuvu_1_18;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  a:array[1..10000] of integer ;
  s,i,n:integer;
begin
  readln(n);
  s:=0;
  for i:=1 to n do
  readln(a[i]);
  for i:=1 to n-2 do
  s:=s+a[i]*a[i+1]*a[i+2] ;
  writeln('s= ',s);
  readln;
end.