n = int(input()) a,b,c,d = input().split() a,b,c,d = int(a),int(b),int(c),int(d) if b-a== c-b == d-c: #等差数列 res = d + (n-4)* (b-a) else: #等比数列 res = d * (n-4) *(b//a) print(res)