a=int(input())
b=input()
n=len(b)
d=[0]
M=10**9+7
for i in range(1,n):
  d+=[pow(a,i,M)-1]
c=0
for v in b:
  c=c*a+int(v)
  c%=M
d+=[c]
for i in reversed(range(1,len(d))):
  d[i]-=d[i-1]
g=0
for i in range(1,n+1):
  g+=i*d[i]
  g%=M
g-=c
g%=M
print(g)