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)