import sys
readline=sys.stdin.readline
from collections import defaultdict

A=int(readline())
B=readline().rstrip()[::-1]
mod=10**9+7
le=len(B)
powA=[1]
for i in range(1,le):
    powA.append(powA[-1]*A%mod)
s=sum(int(b)*powA[i]%mod for i,b in enumerate(B))
ans=0
for i in range(1,le):
    ans+=s-(powA[i]-1)
    ans%=mod
print(ans)