N = int(input())
A = [int(x) for x in input().split()]

A_dup = [x for x in A if A.count(x) > 1]
for a in set(A_dup):
    A_dup.remove(a)
B = list(set(A))

ans = 0
for a in A_dup:
    if max(B) == len(B):
        x = max(B) + 1
    else:
        x = min(set(range(1, max(B))) - set(B))
    ans += x - a
    B.append(max(B) + 1)
print(ans)