{"trustable":false,"prependHtml":"\u003cstyle type\u003d\u0027text/css\u0027\u003e\n .input, .output {\n border: 1px solid #888888;\n }\n .output {\n margin-bottom: 1em;\n position: relative;\n top: -1px;\n }\n .output pre, .input pre {\n background-color: #EFEFEF;\n line-height: 1.25em;\n margin: 0;\n padding: 0.25em;\n }\n \u003c/style\u003e\n \u003clink rel\u003d\"stylesheet\" href\u003d\"//codeforces.org/s/96598/css/problem-statement.css\" type\u003d\"text/css\" /\u003e\n\u003cscript\u003e\n window.katexOptions \u003d {\n delimiters: [\n {left: \u0027$$$$$$\u0027, right: \u0027$$$$$$\u0027, display: true},\n {left: \u0027$$$\u0027, right: \u0027$$$\u0027, display: false},\n {left: \u0027$$\u0027, right: \u0027$$\u0027, display: true},\n {left: \u0027$\u0027, right: \u0027$\u0027, display: false}\n ]\n };\n\u003c/script\u003e\n","sections":[{"title":"Description","value":{"format":"MD","content":"ZWZ和LXL在玩游戏。\n在一个不透光的袋子里,装有r个红球和b个蓝球。\nZWZ和LXL轮流在袋子里拿一个球,ZWZ先手,LXL后手,且在LXL拿出球后,袋子里会随机掉出一个球(若袋子不为空),这个球**不计入**任何人的抽取记录。\n如果拿出来的球是红球,那么拿出这个球的人获胜;若袋子空了,两人也没有抽到红球,则LXL获胜。\n请求出ZWZ获胜的概率。"}},{"title":"Input","value":{"format":"MD","content":"共一行,两个整数r, b(0 \u0026le; r, b \u0026le; 1000)。"}},{"title":"Output","value":{"format":"MD","content":"一个实数,表示ZWZ获胜的概率。答案误差不能超过10\u003csup\u003e-9\u003c/sup\u003e。"}},{"title":"Sample Input","value":{"format":"MD","content":"```5 5```"}},{"title":"Sample Output","value":{"format":"MD","content":"```0.658730159```"}}]}