逆序對數{nlogn,歸排}

var
  n,i:longint;
  ans:int64;
  a,temp:array[1..100000] of longint;
procedure merge(l,m,r:longint);
var
  i,j,k:longint;
begin
  i:=l;
  j:=m+1;
  for k:=l to r do
    begin
      if(i<=m) and ((j>r)or(a[i]<=a[j])) then
       begin
         temp[k]:=a[i];
         inc(i);
       end
     else
       begin
         temp[k]:=a[j];
         inc(j);
         inc(ans,m-i+1);{統計此區間內的逆序對數，若右區間有輸出則將ans加上左區間剩下的個數}
       end;
    end;
  for k:=l to r do a[k]:=temp[k];
end;
procedure sort(l,r:longint);
var
  m:longint;
begin
  m:=(l+r) shr 1;
  if l<>r then
    begin
     sort(l,m);
     sort(m+1,r);
     merge(l,m,r);
    end;
end;
begin
  ans:=0;
  read(n);
  for i:=1 to n do
    read(a[i]);
  sort(1,n);
  writeln(ans);
end.