a , b = input("").split(" ")[:2]
a = int(a)
b = int(b)
d = input("").split(" ")

c = [int(i) for i in d]



lists = []

for i in range(int(a/b)):
    if(b==1):
        break
    for i in range(b):
        lists.append(list())
        lists[i].append(min(c))
        c.remove(min(c))

mex = []

for i in range(b):
    if(b==1):
        break
    min = 0 
    while(min in lists[i]):
        min = min+1
    mex.append(min)
    
if(b==1):
    min = 0
    while(min in c):
        min = min + 1
    
    
   
if(b==1):
    print(min)
else:
    print(sum(mex))