public static void main ( String [ ] args ) {
  Scanner s = new Scanner ( System . in ) ;
  int cnt1 = s . nextInt ( ) ;
  int cnt2 = s . nextInt ( ) ;
  int x = s . nextInt ( ) ;
  int y = s . nextInt ( ) ;
  long l = 0 ;
  long r = ( long ) 1e10 ;
  long mid = 0l ;
  long ans = 0l ;
  while ( l <= r ) {
    mid = l + ( r - l ) / 2 ;
    long forone = mid - mid / x ;
    long fortwo = mid - mid / y ;
    long onlyone = mid / x + mid / y - mid / ( x * y ) ;
    long sub = mid - onlyone ;
    if ( forone >= cnt1 && fortwo >= cnt2 && forone + fortwo - sub >= cnt1 + cnt2 ) {
      ans = mid ;
      r = mid - 1 ;
    }
    else l = mid + 1 ;
  }
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) { Scanner s = new Scanner ( System . in ) ; int cnt1 = s . nextInt ( ) ; int cnt2 = s . nextInt ( ) ; int x = s . nextInt ( ) ; int y = s . nextInt ( ) ; long l = 0 ; long r = ( long ) 1e10 ; long mid = 0l ; long ans = 0l ; while ( l <= r ) { mid = l + ( r - l ) / 2 ; long forone = mid - mid / x ; long fortwo = mid - mid / y ; long onlyone = mid / x + mid / y - mid / ( x * y ) ; long sub = mid - onlyone ; if ( forone >= cnt1 && fortwo >= cnt2 && forone + fortwo - sub >= cnt1 + cnt2 ) { ans = mid ; r = mid - 1 ; } else l = mid + 1 ; } System . out . println ( ans ) ; }
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