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

typedef long long ll;
typedef vector< int > vi;
typedef vector< vi > vvi;
typedef vector< ll > vl;
typedef vector< vl > vvl;
typedef pair< int, int > pii;
typedef vector< pii > vp;
typedef vector< double > vd;
typedef vector< vd > vvd;
typedef vector< string > vs;

template< class T1, class T2 >
int upmin( T1 &x, T2 v ){
  if( x > v ){
    x = v;
    return 1;
  }
  return 0;
}

template< class T1, class T2 >
int upmax( T1 &x, T2 v ){
  if( x < v ){
    x = v;
    return 1;
  }
  return 0;
}

const int INF = 0x3f3f3f3f;

const int MAXN = 20;

int N;
double Pa, Pb;
double A[ MAXN ];
double B[ MAXN ];

void init(){
  cin >> N;
  cin >> Pa >> Pb;
  for( int i = 0; i < N; ++i ){
    cin >> A[ i ];
  }
  for( int i = 0; i < N; ++i ){
    cin >> B[ i ];
  }
}

double dp_a[ 1 << MAXN ][ MAXN ];
double dp_b[ 1 << MAXN ][ MAXN ];
double turn_id_a[ MAXN ][ MAXN ];
double turn_id_b[ MAXN ][ MAXN ];

void build_dp( double p, double a[], double dp[][ MAXN ], double turn_id[][ MAXN ] ){
  for( int i = 0; i < N; ++i ){
    int minv = INF;
    for( int j = 0; j < N; ++j ){
      upmin( minv, a[ j ] );
    }
    if( a[ i ] == minv ){
      dp[ 1 << i ][ i ] = p;
    } else{
      dp[ 1 << i ][ i ] = ( 1.0 - p ) / ( N - 1 );
    }
  }
  for( int s = 1; s < 1 << N; ++s ){
    int minv = INF;
    int n = N - __builtin_popcount( s );
    if( n == 1 ){
      for( int i = 0; i < N; ++i ){
        if( ~s & 1 << i ){
          for( int j = 0; j < N; ++j ){
            if( s & 1 << j ){
              dp[ s | 1 << i ][ i ] += dp[ s ][ j ];
            }
          }
          break;
        }
      }
      continue;
    }
    for( int i = 0; i < N; ++i ){
      if( ~s & 1 << i ){
        upmin( minv, a[ i ] );
      }
    }
    for( int i = 0; i < N; ++i ){
      if( s & 1 << i ){
        for( int j = 0; j < N; ++j ){
          if( ~s & 1 << j ){
            if( a[ j ] == minv ){
              dp[ s | 1 << j ][ j ] += dp[ s ][ i ] * p;
            } else{
              dp[ s | 1 << j ][ j ] += dp[ s ][ i ] * ( 1.0 - p ) / ( n - 1 );
            }
          }
        }
      }
    }
  }
  for( int s = 1; s < 1 << N; ++s ){
    int turn = __builtin_popcount( s ) - 1;
    for( int i = 0; i < N; ++i ){
      turn_id[ turn ][ i ] += dp[ s ][ i ];
    }
  }
}

void preprocess(){
  build_dp( Pa, A, dp_a, turn_id_a );
  build_dp( Pb, B, dp_b, turn_id_b );
}

void solve(){
  double ans = 0.0;
  for( int turn = 0; turn < N; ++turn ){
    for( int i = 0; i < N; ++i ){
      for( int j = 0; j < N; ++j ){
        if( A[ i ] <= B[ j ] ) continue;
        ans += turn_id_a[ turn ][ i ] * turn_id_b[ turn ][ j ] * ( A[ i ] + B[ j ] );
      }
    }
  }     
  cout << fixed << setprecision( 10 ) << ans << endl;
}

signed main(){
  ios::sync_with_stdio( 0 );
  init();
  preprocess();
  solve();
  return 0;
}