Check whether a given matrix is upper triangle or not

 m=int(input("Size of matrix"))

a=[]

for i in range(m):

    a.append([int(j) for j in input().split()])  

flag=0

for i in range(1,len(a)):

    for j in range(i):

        if a[i][j]!=0:

            flag=1

            break

        

if flag:

    print("not Upper")

else:

    print("Upper traingle")