�了终点。<b>若到不了终点，则步数视为无穷大。</b>但你必须想方设法求出Morenan所走步数的期望值。</span></div></div></div></div></div><div class="row"><div class="column"><h4 class="ui top attached block header">输入格式</h4><div class="ui bottom attached segment font-content"><div style="position: relative; overflow: hidden;"><div class=content><div style="text-indent: 21pt" align="left"><span style="font-size: medium">第1行4个整数，N,M,S,T</span></div>
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