mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    a = int(input())
    B = input().rstrip('\n')
    B = list(map(int, B))

    bb = 0
    for i in range(len(B)):
        bb = (bb + B[-i-1] * (pow(a, i, mod))%mod)%mod
    ans = 0
    for i in range(len(B)):
        if i == len(B) - 1:
            ans = (ans + i * (bb - pow(a, i, mod) + 1))%mod
        else:
            ans = (ans + i * (a-1) * pow(a, i, mod))%mod
    print(ans)


if __name__ == '__main__':
    main()