CF773A Success Rate

You are an experienced Codeforces user. Today you found out that during your activity on Codeforces you have made $ y $ submissions, out of which $ x $ have been successful. Thus, your current success rate on Codeforces is equal to $ x/y $ . Your favorite rational number in the $ [0;1] $ range is $ p/q $ . Now you wonder: what is the smallest number of submissions you have to make if you want your success rate to be $ p/q $ ?

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In the first example, you have to make 4 successful submissions. Your success rate will be equal to $ 7/14 $ , or $ 1/2 $ . In the second example, you have to make 2 successful and 8 unsuccessful submissions. Your success rate will be equal to $ 9/24 $ , or $ 3/8 $ . In the third example, there is no need to make any new submissions. Your success rate is already equal to $ 20/70 $ , or $ 2/7 $ . In the fourth example, the only unsuccessful submission breaks your hopes of having the success rate equal to 1.