Python error IndexError list index out of range

Question

I am trying to execute the following python code:

def construct(s, k, a):
    index = 0
    # Finding the index which is not -1
    for i in range(s):
        if (a[i]!=-1):
            index = i
            break
    # Calculating the values of the indexes index-1 to 0
    for i in range(index-1, -1, -1):
        if (a[i]==-1):
            a[i]=(a[i + 1]-1 + k)% k
    # Calculating the values of the indexes index + 1 to n
    for i in range(index + 1, s):
        if(a[i]==-1):
            a[i]=(a[i-1]+1)% k
            print(a)
# Driver code
s, k = 6, 7
a = [1, 2, 3, 4, 5]
construct(s, k, a)

I get the following error:

IndexError: list index out of range