#include<stdio.h>
int  main()

{int k;
scanf("%d",&k);
printf ("输入需要计算的值\n");
double a, b, result;
scanf("%lf%lf",&a,&b);

switch( k)
    {
    case 1: result=a+b; break;
    case 2: result=a-b; break;
    case 3: result=a*b; break;
    case 4: result=a/b; break;
}
        printf("%lf\n",result);
        return 0;}