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

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

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;
}

int H, A, D;

void init(){
  cin >> H >> A >> D;
}

vi vis;
vd dp;

void preprocess(){
  vis = vi( H + 1 );
  dp = vd( H + 1 );
}

double dfs( int h ){
  if( h <= 0 )
    return 0;
  if( vis[ h ] )
    return dp[ h ];
  vis[ h ] = 1;
  return dp[ h ] = min( dfs( h - A ) + 1, dfs( h ) / 2 + dfs( h - D ) + 3.0 / 2 );
}

void solve(){
  cout << dfs( H ) << endl;
}

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