Formula with IF conditions

Problem is I need to create a forumla in "one" cell, A2, that is dependent on a value entered in cell A1. Example: If data entered in A1 = A, then sum the values in B1 and C1, however if the data in A1 = B, then sum the values in D1 and E1, unless the data in A1 = C, then sum the values in F1 and G1, otherwise put an "X" in cell A2. Is there a limit on the number of variables that can be entered in cell A1? In Lotus (DOS)the formula is: if(A1=A,(B1+C1),@if(A1=B,(C1+D1),@if(A1=C,(D1+E1),"X"))). Your help is very much anticipated and appreciated. Thank You