missing.py

# getMissingNo takes list as argument
def getMissingNo(A):
    n = len(A)
    total = (n+1)*(n+2)/2
    sum_of_A = sum(A)
    return total - sum_of_A
 
# Driver program to test above function
A = [1, 2, 4, 5, 6]
miss = getMissingNo(A)
print(miss)