<span>Dog</span><span style="font-family:宋体;">同学喜欢去购物，但是他不想花很多钱，所以他总是挑那些打折的东西来买，现在给出他买的所有东西的一个购物清单，以及每个物品打几折，问他这次购物一共花了多少钱？</span>

<span></span>

<span style="font-family:宋体;">输入文件（</span><span>money.in</span><span style="font-family:宋体;">）</span>

<span style="font-family:宋体;">第一行一个</span><span>n(1&lt;=n&lt;=100)</span><span style="font-family:宋体;">表示</span><span>dog</span><span style="font-family:宋体;">一共买了多少个东西。</span>

<span style="font-family:宋体;">后面紧接</span><span>n</span><span style="font-family:宋体;">行，每行描述购买的一种物品：</span>

<span style="font-family:宋体;">每行</span><span>2</span><span style="font-family:宋体;">个整数</span><span>ai</span><span style="font-family:宋体;">，</span><span>bi</span><span style="font-family:宋体;">（</span><span>1&lt;=ai&lt;=10000,1&lt;=bi&lt;=10</span><span style="font-family:宋体;">）</span><span>,</span><span style="font-family:宋体;">分别表示物品的原价及该物品的折头。</span>

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<span style="font-family:宋体;">输出文件（</span><span>money.out</span><span style="font-family:宋体;">）</span>

<span style="font-family:宋体;">一行，一个实数为</span><span>dog</span><span style="font-family:宋体;">一共花了多少钱，答案保留</span><span>2</span><span style="font-family:宋体;">位小数</span>

<span><br />

样例

<span>Input</span><span style="font-family:宋体;">：</span>

<span>2</span>

<span>10000 10</span>

<span>1 1</span>

<span></span>

<span>Output</span><span style="font-family:宋体;">：</span>

<span>10000.10</span>