mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    A = list(map(int, input().split()))
    A_set = set(A)
    ans = 0
    for a in A:
        if a-1 not in A:
            ans += a
    print(ans)


if __name__ == '__main__':
    main()