A=int(input())
B=input()
mod=10**9+7
N=len(B)
ANS=0
X=A-1
for i in range(N-1):
  ANS+=X*i
  X=X*A%mod
ANS%=mod
C=int(B[0])-1
for i in range(1,N):
  C=(C*A+int(B[i]))%mod
C+=1
print((ANS+C*(N-1))%mod)