N = int(input())
L = [list(map(str,input().split())) for i in range(N)]

A = [True for i in range(N)]

for i in range(N) :
    for j in range(N) :
        if i == j :
            continue
        elif L[i][j] != "nyanpass" :
            A[j] = False
if A.count(True) != 1 :
    print(-1)
else :
    print(A.index(True)+1)