HI all
For solving this problem use dynamic programming
as this way:
  for finding answer of k... do it:
    for i:=1 to k do
      f[k]:=f[k]+c(i,k)*f[k-i];
which c(i,k) is amount of ways to choose i thing from k thing:
  c(i,k)= k! / (i!*(k-i)!)
ans its proof is:
variable i is amount of '='s that use
if 1time '=' use then it we should choose 2 operand in both sides of
= operator
and if 2= uses then we should chose 3operand (form k operand that we
have)...
ans etc.
mail me for more explaination:
aidin_n7@hotmail.com