public static void main ( String [ ] args ) {
  InputReader in = new InputReader ( System . in ) ;
  long r ;
  int x , y , xx , yy ;
  r = in . nextInt ( ) ;
  x = in . nextInt ( ) ;
  y = in . nextInt ( ) ;
  xx = in . nextInt ( ) ;
  yy = in . nextInt ( ) ;
  r *= 2 ;
  long dist = ( x - xx ) * 1L * ( x - xx ) + ( y - yy ) * 1L * ( y - yy ) ;
  r *= r ;
  int L = 0 , R = 1000000 ;
  while ( R > L ) {
    int mid = L + ( R - L ) / 2 ;
    BigInteger temp = BigInteger . valueOf ( mid ) ;
    temp = temp . multiply ( BigInteger . valueOf ( mid ) ) ;
    temp = temp . multiply ( BigInteger . valueOf ( r ) ) ;
    int test = temp . compareTo ( BigInteger . valueOf ( dist ) ) ;
    if ( test == 0 || test == 1 ) R = mid ;
    else L = mid + 1 ;
  }
  System . out . println ( R ) ;
}

public static void main ( String [ ] args ) { InputReader in = new InputReader ( System . in ) ; long r ; int x , y , xx , yy ; r = in . nextInt ( ) ; x = in . nextInt ( ) ; y = in . nextInt ( ) ; xx = in . nextInt ( ) ; yy = in . nextInt ( ) ; r *= 2 ; long dist = ( x - xx ) * 1L * ( x - xx ) + ( y - yy ) * 1L * ( y - yy ) ; r *= r ; int L = 0 , R = 1000000 ; while ( R > L ) { int mid = L + ( R - L ) / 2 ; BigInteger temp = BigInteger . valueOf ( mid ) ; temp = temp . multiply ( BigInteger . valueOf ( mid ) ) ; temp = temp . multiply ( BigInteger . valueOf ( r ) ) ; int test = temp . compareTo ( BigInteger . valueOf ( dist ) ) ; if ( test == 0 || test == 1 ) R = mid ; else L = mid + 1 ; } System . out . println ( R ) ; }
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