练习程序，问题如下：进行高精度整数的加、减、乘运算。输入两个十进制大整数M和N（M、N最长可达50位），计算运算结果并输出。【输入形式】标准输入上依次分行输入以下内容：1.第一行输入第一个大整数M。M可能带有负号，后面是最长可达50位的数字序列。2.第二行只有一个字符，可以是“+”、“-”、“*”，分别代表加、减、乘三种运算符。3. 第三行输入大整数N，格式与M相同M、N均不带有前缀的多余的0【输出形式】在标准输出上打印运算结果，输出一行字符序列，是大整数M和N和运算结果。如果该运算结果是正数，则直接输出各位数字序列；如果是负数，则首先要输出负号。各位数字紧密输出，不带有前缀的多余的0。-practice procedures, as follows : high-precision integer for the addition, subtraction, multiplication. The importation of two decimal integer big M and N (M, N up to a maximum of 50), the calculated results of operations and output. Entry forms : standard input on the importation of branches were the following : 1. The first line inputs, a large integer M. M may have negative, is back up to 50 digital sequence. 2. Only a second line of characters could be "","-","*", respectively, plus or minus, by three operators. 3. The third line inputs large integer N, M and the same format M, N are not redundant with the prefix 0 output -- in the form of print on standard output Operational result, the output sequences of characters here is the large integers M and N and