def su2(k,l):
    a=k+l
    if a>9:
        r=a%10
        a=1+r
    return a
T=int(input())
S=[list(i) for i in input().split()]
for i in range(T):
    for j in range(len(T[i])):
        T[i][j]=int(T[i][j])
    for j in range(len(T[i])-3):
        for k in range(1,len(T[i])-j-1):
            T[i][k-1]=su2(T[i][k-1], T[i][k])
    T[i][0]=su2(T[i][0],T[i][1])
print(T[i][0])