This problem is in Contest(s) below:
Contest 1980:语法基础-顺序结构练习-(4)数学函数练习
Contest 1981:期末考试
Contest 1984:寒假练习（一）
Contest 1993:寒假练习（一）复现
Contest 1994:寒假练习（二）复现
Contest 1985:寒假练习（二）