MOD=10**9+7
a=int(input())
b=input()
n=len(b)
ans=0
tmp=0
curr=1
for i in range(n):
  k=int(b[n-1-i])
  if i<n-1:
    ans=(ans+i*curr*(a-1))%MOD
  else:
    ans=(ans+i*curr*(k-1))%MOD
  if i<n-1:
    tmp+=(curr*k)%MOD
  curr=(curr*a)%MOD

ans=(ans+(tmp+1)*(n-1))%MOD
print(ans)