import sys

sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


A = I()
mod = 10**9+7
B = S()
N = len(B)

A_power = [1]
for _ in range(N):
    A_power.append((A_power[-1]*A) % mod)

ans = 0
for i in range(N-1):
    ans += i*(A_power[i+1]-A_power[i])
    ans %= mod

a = 0
for i in range(N-1,-1,-1):
    a += int(B[i])*A_power[N-1-i]
    a %= mod

ans += (a-A_power[N-1]+1)*(N-1)
ans %= mod
print(ans)