#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/multiprecision/number.hpp>
using namespace boost::multiprecision;
using mint=modint1000000007;

#define tpf typedef
tpf double db;tpf long long ll;
tpf string str;tpf vector<ll> vll;
tpf vector<str> vs;tpf pair<ll,ll> pll;
tpf vector<pll> vpll;tpf vector<vll> vvll;
tpf cpp_int cp;tpf complex<db> com;
tpf vector<bool> vb;

int a,b;
#define For(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) For(i,0,n)
#define F first
#define S second
#define psf push_front
#define psb push_back
#define epb emplace_back
#define mkp make_pair
#define All(x) x.begin(),x.end()
#define Alld(x) All(x),greater<>()
#define dupde(x) x.erase(unique(All(x)),x.end())
#define nxp next_permutation
#define sep setprecision
#define lob lower_bound
const int mod = 1000000007;const ll INF=1e17;
const db pi=acos(-1);
const int di[]={-1,0,1,0};
const int dj[]={0,-1,0,1};
ll gcd(ll x,ll y){return y? gcd(y,x%y):x;}
ll ncr(ll n,ll r){
  ll x=1,y=1;rep(i,r){x*=(n-i);y*=(i+1);}
  return x/y;
}
mint modncr(ll n,ll r){
mint x=1,y=1;r=min(n-r,r);
rep(i,r){x*=(n-i);y*=(i+1);}
return x*y.inv();
}
ll pncr(ll n,ll r){
vvll v(n+1,vll(n+1));v[0][0]=1;
rep(i,n)rep(j,i+1){
v[i+1][j]+=v[i][j];
v[i+1][j+1]+=v[i][j];
}
return v[n][r];
}
template<class T> inline bool chmin(T& a, T b){
  if(a>b){a=b;return true;}return false;
}
template<class T> inline bool chmax(T& a, T b){
  if(a<b){a=b;return true;}return false;
}
ll to_base(ll n,ll i){
  string s;
  while(n){s=to_string(n%i)+s;n/=i;}
  ll a=stoll(s);return a;
}
ll prime(ll n){
  if(n==2)return 1;
  if(n%2==0||n==1)return 0;
  for(ll i=3;i*i<=n;i+=2)if(n%i==0)return 0;
  return 1;
}
vll divisor(ll n){
  vll a;
  for(ll i=1;i*i<=n;i++){
    if(n%i==0){
      a.psb(i);if(i!=n/i)a.psb(n/i);
    }
  }
  sort(All(a));return a;
}
vector<pair<ll,ll>> prifac(ll n){
  vector<pair<ll,ll>> a;
  for(ll i=2;i*i<=n;i++){
    if(n%i!=0){continue;}ll exp=0;
    while(n%i==0){n/=i;exp++;}
    a.psb(pll(i,exp));
  }
  if(n!=1){a.psb(pll(n,1));}return a;
}
vll cumsum(vll a){
  ll sz=a.size();
  vll dp(sz+1);
  rep(i,sz)dp[i+1]=dp[i]+a[i];
  return dp;
}
vll eratos(ll n){
  vll f(n+1),p;
  rep(i,n+1)f[i]=1;
  For(i,2,n+1){
    if(f[i]){
      for(ll j=2*i;j<=n;j+=i)f[j]=0;
      p.psb(i);
    }
  }
 return p;
}
vll eratos2(vll a,ll n){
  vb x(n),ok(n,true);vll p,res;
  for(ll i:a)x[i]=true;
  For(i,2,n){
    bool f=false;
    for(ll j=i;j<n;j+=i)if(x[j])f=true;
    if(f)p.psb(i);
  }
  for(ll i:p){
    for(ll j=i;j<n;j+=i){
      ok[j]=false;
    }
  }
  For(i,1,n)if(ok[i])res.psb(i);
  return res;
}
ll eulerf(ll n){
  vll v(1);v[0]=n;
  vll res=eratos2(v,n+1);
  return res.size();
}
ll eulerf2(ll n){
  vpll a=prifac(n);ll res=n;
  for(auto i:a){res*=i.F-1;res/=i.F;}
  return res;
}

int main(){
  ios::sync_with_stdio(0);
  cin.tie(0);
  ll a,ans=0,c=0;str b;cin>>a>>b;
  ll n=b.size();
  vll v(n);reverse(All(b));
  v[0]=1;n%=mod;
  rep(i,n-1){
    v[i+1]=v[i]*a%mod;
  }
  rep(i,n){
    c+=v[i]*(b[i]-'0')%mod;
    c%=mod;
  }
  For(i,1,n){
    ans+=(i-1)*(v[i]-v[i-1])%mod;
    ans%=mod;
  }
  ans+=(n-1)*(c-v[n-1]+1)%mod;
  cout<<(ans+2*mod)%mod;
  return 0;
}