def szamolas(N: int, K: int, dij: list):
    varosok=0
    eredmeny=0
    for i in range(0, len(dij)):
        if dij[i]==1:
            varosok=varosok+1
    if varosok==0 or varosok==1:
        return 0
    else:
        for i in range(2, K+1):
            if i>varosok:
                break
            eredmeny=eredmeny+(varosok-(i-1))
    return eredmeny

def test():
    a=szamolas(10, 3, [0, 1, 1, 0, 0, 0, 1, 1, 0, 1])
    assert a==7

    a=szamolas(5, 5, [0, 1, 0, 0, 0])
    assert a==0

    a=szamolas(6, 5, [1, 0, 1, 0, 1, 0])
    print(a)
    assert a==3
    
    a=szamolas(15, 5, [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1])
    print(a)
    assert a==50
    
    a=szamolas(2, 2, [1, 1])
    print(a)
    assert a==1


def futtatas():
    N, K=map(int, input().split())
    dij=list(map(int, input().split()))
    a=szamolas(N, K, dij)
    print(a)

#test()
futtatas()