import sys
input = sys.stdin.readline
N, M = map(int, input().split())
A = list(map(int, input().split()))
ans = 0
for i in range(M-1):
    gap = A[i+1]-A[i]
    cnt = 1
    while True:
        if gap==2:
            ans += cnt
            break
        elif gap%2!=0:
            ans += (gap-1)*cnt
            break
        else:
            gap//=2
            cnt*=2
    
print(ans)