from collections import deque

def sousa(N, li):
    pasd = deque()
    movd = deque()
    pasd.append(li[0])
    for i in range(1, len(li)):
        if li[i] < pasd[-1]:
            movd.append(li[i])
        elif li[i] == pasd[-1] + 1:
            pasd.append(li[i])
        elif li[i] > pasd[-1] + 1:
            for j in range(len(pasd)):
                movd.append(pasd[j])
            pasd = deque()
            pasd.append(li[i])
    result = len(movd)
    return result

def main():
    N = int(input())
    li = list(map(int, input().split()))
    print(sousa(N, li))

if __name__ == '__main__':
    main()