9 13
6 14 19 5 -5 6 -10 20 8
 8 9
6 -1 5 -5 -8 -7 -8 -7
 10 7
-9 3 -4 -22 4 -17 0 -14 3 -2
 6 2
-2 3 0 -2 0 0
 5 10
-8 -24 0 -22 12
 5 13756
-2 -9 -10 0 10
 7 3
1 -3 0 3 -1 0 2
 9 9
-3 2 0 -2 -7 -1 0 5 3
 2 3
2 0
 19 78701
1 0 -1 0 -1 -1 0 1 0 -1 1 1 -1 1 0 0 -1 0 0
 5 4
-1 0 0 1 -1
 6 4
-1 0 2 -4 0 5
 20 23036
-1 1 -1 -1 -1 -1 1 -1 -1 0 0 1 1 0 0 1 0 0 -1 -1
 5 4
-1 0 -3 0 3
 12 82016
1 -2 -1 -1 -2 -1 0 -2 -1 1 -2 2
 7 4
-6 0 2 -3 0 4 0
 4 4
2 2 0 1
 6 1
-3 0 0 0 -2 3
 8 26
-4 9 -14 -11 0 7 23 -15
 20 23079
0 1 1 -1 1 0 -1 -1 0 0 1 -1 1 1 1 0 0 1 0 1
 1 1
1
 7 8555
-2 -3 -2 3 0 -2 0
 4 100
-100 0 -50 100
 3 14
12 12 -8
 1 1
2
 10 23
9 7 14 16 -13 -22 24 -3 -12 14
 8 11
12 -12 -9 3 -22 -21 1 3
 19 49926
-2 0 2 0 0 -2 2 -1 -1 0 0 0 1 0 1 1 -2 2 2
 16 76798
-1 11 -7 -4 0 -11 -12 3 0 -7 6 -4 8 6 5 -10
 9 5
-2 0 3 -4 0 4 -3 -2 0

-1
 -1
 1
 1
 1
 1
 -1
 2
 0
 1
 1
 -1
 1
 1
 1
 1
 -1
 1
 -1
 0
 0
 1
 1
 -1
 -1
 -1
 -1
 1
 1
 1

from sys import stdin
rr = lambda: stdin.readline().strip()
rri = lambda: int(rr())
rrm = lambda: map(int, rr().split())

debug=0
if debug:
    fi = open('t.txt','r')
    rr = lambda: fi.readline().replace('\n','')

import itertools
def parse(A):
    su = maxi = 0
    for x in A:
        maxi = max(maxi, su)
        su += x
    return su, max(maxi, su)

def solve(N, D, A):
    NOPE = -1
    CHECK = 'check'
    groups = []
    for k,g in itertools.groupby(A, bool):
        if k:
            groups.append(parse(list(g)))
        else:
            groups.append(CHECK)
    #while groups and groups[-1] != CHECK:
    #    groups.pop()
    while groups and groups[0] == CHECK:
        groups.pop(0)
    
    bal = [0, 0]
    ans = 0
    for i, grp in enumerate(groups):
        if grp != CHECK and i+1<len(groups) and groups[i+1] == CHECK:
            su, top = grp
            ceiling = D - top
            if bal[0] <= ceiling and min(ceiling, bal[1]) + su >= 0:
                bal[1] = min(bal[1], ceiling)
                bal[0] = max(bal[0], -su)
                bal[0] += su
                bal[1] += su
                continue
            elif bal[0] <= ceiling:
                bal = [0, D]
                ans += 1
            else:
                return NOPE
        elif grp != CHECK:
            su, top = grp
            ceiling = D - top
            if bal[0] > ceiling:
                return NOPE
            
    return ans

N, D = rrm()
A = rrm()
print solve(N, D, A)
