fin = open('count.in', 'r')
fout = open('count.out', 'w')


n = int(input())
a = [[int(x) for x in fin.readline().split()] for _ in range(n)]
count = 0
for i in range(n):
    for j in range(n):
        if a[i][j] == 1:
            count += 1
print(count // 2, file = fout)