public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int c = sc . nextInt ( ) ;
  int v0 = sc . nextInt ( ) ;
  int v1 = sc . nextInt ( ) ;
  int a = sc . nextInt ( ) ;
  int l = sc . nextInt ( ) ;
  int xx = v0 ;
  int pos = v0 ;
  int t = 1 ;
  while ( pos < c ) {
    xx = Math . min ( v1 , xx + a ) ;
    pos += xx - l ;
    t ++ ;
  }
  System . out . println ( t ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int c = sc . nextInt ( ) ; int v0 = sc . nextInt ( ) ; int v1 = sc . nextInt ( ) ; int a = sc . nextInt ( ) ; int l = sc . nextInt ( ) ; int xx = v0 ; int pos = v0 ; int t = 1 ; while ( pos < c ) { xx = Math . min ( v1 , xx + a ) ; pos += xx - l ; t ++ ; } System . out . println ( t ) ; }
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