import math
A = int(input())

B = input()
logB = len(B)-1
B = int(B, A)

MOD = 10**9+7

# logB = int(math.log(B, A))
ans = 0
now = (A-1)
for i in range(1, logB+1):
    if i == logB:
        now = B-(pow(A, logB))+1
    else:
        now *= A
    ans = (ans+i*now % MOD) % MOD

print(ans)