N=int(input())
S=input()
T=S[N-1]
z=0
if T=="x":
for i in range(N-2,-1,-1):
if N%2==0 and i%2==0 or N%2==1 and i%2==1:
z+=(2*int(S[i]))%10+(2*int(S[i]))//10
else:
z+=int(S[i])
print(z*9%10)
else:
m=0
T=int(T)
x=0
for i in range(N-2,-1,-1):
if S[i]!="x" and (N%2==0 and i%2==0 or N%2==1 and i%2==1):
z+=(2*int(S[i]))%10+(2*int(S[i]))//10
elif S[i]!="x":
z+=int(S[i])
if S[i]=="x":
m=i
if z%10<T:
x=T-z%10
elif z*9%10==T:
x=0
else:
x=10+T-z%10
if N%2==0 and m%2==0 and x!=1 or N%2==1 and m%2==1 and x!=1:
x//=2
print(x)
