a = int(input())
b = list(str(input()))
b.reverse()
mod = 10**9+7
N = 2*10**5
P = [0]*N
P[0] = 1
for i in range(1,N):
    P[i] = P[i-1]*a
    P[i] %= mod
s = 0
for i in range(len(b)):
    s += P[i]*int(b[i])
    s %= mod
ans = 0
for i in reversed(range(len(b))):
    if i == len(b)-1:
        ans += (s-P[i]+1)*i
        ans %= mod
    else:
        ans += (P[i+1]-P[i])*i
        ans %= mod
print(ans)