MOD = 10**9+7
a = int(input())
b = input()
n = len(b)
ans = 0
r = 1
for i in range(n-1):
    ans += i*r*(a-1)%MOD
    r = r*a%MOD
v = 0
for i in map(int,b):
    v = (v*a+i)%MOD
ans += (n-1)*(v-r+1)
print(ans%MOD)