n = int(input())
x = list(map(int, input().split()))

# Check for duplicates
if len(set(x)) != n:
    print("NO")
else:
    x_sorted = sorted(x)
    min_val = x_sorted[0]
    max_val = x_sorted[-1]
    total_diff = max_val - min_val

    # Check if total difference can be evenly divided by (n-1)
    if total_diff % (n - 1) != 0:
        print("NO")
    else:
        d = total_diff // (n - 1)
        # Check each consecutive pair
        valid = True
        for i in range(1, n):
            if x_sorted[i] - x_sorted[i-1] != d:
                valid = False
                break
        print("YES" if valid else "NO")