#include<stdio.h>
#include<iostream>
using namespace std;
int main(){
    ios::sync_with_stdio(false);
    int a, b;
    short x;
    char c;
    cin >> a >> b >> c;
    x = int(c) - 42;
    switch(x){
        case 0:
            cout << a*b;
            break;
        case 1:
            cout << a+b;
            break;
        case 3:
            cout << a-b;
            break;
        case 5:
            printf("%.2lf", double(a)/double(b));
            break;
    }
    return 0;
}

为啥全WA?!