【 輪盤專弈：若何在這個遊戲中後退勝算機會？】

SyntaxError: Unexpected token < in JSON at position 0
    at JSON.parse (<anonymous>)
    at /root/rankerxmobiledoc/index.js:67:55
    at Layer.handle [as handle_request] (/root/rankerxmobiledoc/node_modules/express/lib/router/layer.js:95:5)
    at next (/root/rankerxmobiledoc/node_modules/express/lib/router/route.js:144:13)
    at Route.dispatch (/root/rankerxmobiledoc/node_modules/express/lib/router/route.js:114:3)
    at Layer.handle [as handle_request] (/root/rankerxmobiledoc/node_modules/express/lib/router/layer.js:95:5)
    at /root/rankerxmobiledoc/node_modules/express/lib/router/index.js:284:15
    at Function.process_params (/root/rankerxmobiledoc/node_modules/express/lib/router/index.js:346:12)
    at next (/root/rankerxmobiledoc/node_modules/express/lib/router/index.js:280:10)
    at /root/rankerxmobiledoc/node_modules/body-parser/lib/read.js:137:5