import math n, k = map(int,input().split()) a = list(map(int,input().split())) l = 6350400 if(n == 1): print("1/1") exit() if(k == 1): print("0") exit() p = q = 0 for i in range(k - 1): p += l // (a[i] * a[i + 1]) for i in range(n - 1): q += l // (a[i] * a[i + 1]) l = math.gcd(p, q) p //= l q //= l assert (p < 10**9) assert (q < 10**9) print(str(p) + '/' + str(q))