A = int(input())
B = input()
mod = 10**9 + 7
N = len(B)
b = int(B,A)
ans = (b - pow(A,N-1)+1)*(N-1)%mod
for j in range(1,N-1):
    ans += j*(pow(A,j+1,mod) - pow(A,j,mod))
    ans %= mod
print(ans)