Write a program that prints the maximum element in the area below the main diagonal including the diagonal of the square matrix.

#input:
# 3
# 1 2 3
# 4 5 6
# 7 8 9
# output:
# 18

n = int(input())
matrix = [list(map(int, input().split())) for _ in range(n)]

result = 0
for i in range(n):
  for j in range(n):
    if i + j >= n:
      break
    result += matrix[i][j]

print(result)