Bobo lives in an infinite chessboard. Initially he locates at . There are 4 buttons. When the first button is pressed, Bobo moves right for at most a cells. When the second button is pressed, Bobo moves up for at most b cells. When the third button is pressed, Bobo moves left for at most c cells. When the fourth button is pressed, Bobo moves down for at most d cells. Find the number of cells Bobo can reach modulo , if he presses the buttons for no more than n times.
Bobo lives in an infinite chessboard. Initially he locates at (0, 0). There are 4 buttons. When the first button is pressed, Bobo moves right for at most a cells. When the second button is pressed, Bobo moves up for at most b cells. When the third button is pressed, Bobo moves left for at most c cells. When the fourth button is pressed, Bobo moves down for at most d cells. Find the number of cells Bobo can reach modulo (109+7)(10^9+7)(109+7), if he presses the buttons for no more than n times.
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