n=gets.to_i
mat=[]

n.times{
    mat+=[gets.split(" ").map{|e| (e=="-" || e=="nyanpass")}]
}

mat = mat.transpose

target=-2
n.times{|i|
    if mat[i].inject(:&)
        if 0<=target
            puts "-1";exit(0)
        end
        target=i
    end
}

puts target+1