#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define pre(i,a,b) for(int i=a;i>=b;i--)
#define N 20
using namespace std;
char c[N];int k;
int u[N],v[N],s[N],t[N],a[N],b[N];
int Pow(int x,int y){
	int now=1;
	for(;y;y>>=1,x=x*x)if(y&1)now=now*x;
	return now;
}
bool check(){
	long long ans=0;
	memset(a,0,sizeof(a));
	memset(b,0,sizeof(b));
	rep(i,1,5)a[s[i]]++,b[t[i]]++;
	rep(i,1,9)ans+=i*Pow(10,a[i])-i*Pow(10,b[i]);
	return ans>0;
}
int main(){
	scanf("%d",&k);
	scanf("%s",c+1);
	rep(i,1,4)s[i]=c[i]-'0';
	scanf("%s",c+1);
	rep(i,1,4)t[i]=c[i]-'0';
	rep(i,1,4)u[s[i]]++,u[t[i]]++;
	double ans=0;
	for(s[5]=1;s[5]<=9;s[5]++)for(t[5]=1;t[5]<=9;t[5]++)if(check()){
		ans+=1.00*(k-u[s[5]])/(9*k-8)*(k-u[t[5]]-(t[5]==s[5]))/(9*k-9);
	}
	printf("%lf\n",ans);
	return 0;
}
//#define _GLIBCXX_DEBUG

#include<bits/stdc++.h>
using namespace std;

#define endl '\n'
#define lfs cout<<fixed<<setprecision(10)
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define fi first
#define se second
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define EB emplace_back
#define rep(i,n,m) for(ll i = (n); i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = (ll)(m) - 1; i >= (ll)(n); i--)
using ll = long long;
using ld = long double;
const ll MOD1 = 1e9+7;
const ll MOD9 = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template<typename T1, typename T2>bool chmin(T1 &a,T2 b){if(a>b){a=b;return true;}else return false;}
template<typename T1, typename T2>bool chmax(T1 &a,T2 b){if(a<b){a=b;return true;}else return false;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++){cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>&v,ll h,ll w){for(ll i=0;i<h;i++){for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>void debug(vector<T>&v,ll n){if(n!=0)cout<<v[0];for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>vector<vector<T>>vec(ll x, ll y, T w){vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
vector<ll>dx={1,-1,0,0,1,1,-1,-1};vector<ll>dy={0,0,1,-1,1,-1,1,-1};
template<typename T>vector<T> make_v(size_t a,T b){return vector<T>(a,b);}
template<typename... Ts>auto make_v(size_t a,Ts... ts){return vector<decltype(make_v(ts...))>(a,make_v(ts...));}
template<typename T1, typename T2>ostream &operator<<(ostream &os, const pair<T1, T2>&p){return os << p.first << " " << p.second;}
template<typename T>ostream &operator<<(ostream &os, const vector<T> &v){for(auto &z:v)os << z << " ";cout<<"|"; return os;}
template<typename T>void rearrange(vector<ll>&ord, vector<T>&v){
  auto tmp = v;
  for(int i=0;i<tmp.size();i++)v[i] = tmp[ord[i]];
}
template<typename Head, typename... Tail>void rearrange(vector<ll>&ord,Head&& head, Tail&&... tail){
  rearrange(ord, head);
  rearrange(ord, tail...);
}
//mt19937 mt(chrono::steady_clock::now().time_since_epoch().count());
int popcount(ll x){return __builtin_popcountll(x);};
int poplow(ll x){return __builtin_ctzll(x);};
int pophigh(ll x){return 63 - __builtin_clzll(x);};

int main(){
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  ll res=0,buf=0;
  bool judge = true;
  ll n;cin>>n;
  ll k=1<<n;
  ll m=k-1;
  //vector<string>ret(m,string(k,'B'));
  vector<string>ret(1,"AB");
  rep(i,1,n){
    vector<string>nret((1<<i+1)-1,string(1<<i+1,'B'));
    rep(j,0,ret.size()){
      rep(o,0,ret[j].size()){
        if(ret[j][o]=='A'){
          nret[j][o]='A';
          nret[j][o|1<<i]='A';
          nret[j+ret.size()][o]='A';
        }
        if(ret[j][o]=='B'){
          nret[j+ret.size()][o|1<<i]='A';
        }
      }
    }
    /*rep(j,ret.size(),nret.size()){
      ll dif=j-(ll)ret.size();
      //rep(o,0,1<<i)nret[j][(dif+o)%(1<<i+1)]='A';
      rep(o,0,1<<i)nret[j][o]='A';
      swap(nret[j][dif],nret[j][dif+(1<<i)]);
    }*/
    rep(o,0,1<<i)nret.back()[o]='A';
    ret=nret;
  }
  cout<<m<<endl;
  debug(ret,m,k);
  /*ll pos=3;
  vector<ll>cnt(k);
  rep(i,0,m)rep(j,0,k){
    if(ret[i][j]==ret[i][pos])cnt[j]++;
  }
  debug(cnt,k);*/
  return 0;
}