program operatii;
var f,g:text;
    v:array[1..1000002]of longint;
    n,i:longint;
    c:int64;
begin
assign(f,'operatii.in');
assign(g,'operatii.out');
reset(f);
rewrite(G);
read(f,n);
c:=0;
for i:=1 to n do
  read(f,v[i]);
for i:=1 to n do
  if (v[i]>v[i+1])then
    c:=c+v[i]-v[i+1];
write(g,c);
close(f);
close(g);
end.