def fn(arr,d):
    cnt=0
    s=0
    curr=0
    for i in range(len(arr)):
        if i==0:
            s=arr[i]
            curr=arr[i]
            cnt=1
        else:
            diff=arr[i]-arr[i-1]
            if diff==d:
                s+=(arr[i]*(cnt+1)+curr)
                curr+=arr[i]*(cnt+1)
                cnt+=1
            else:
                s+=arr[i]
                curr=arr[i]
                cnt=1
    
    return s
    
def main(arr):
    suma=0
    for x in arr:
        suma+=x
    
    return fn(arr,0)+fn(arr,1)-suma


arr=[5,8,8,10,11,12]
print(main(arr))