头文件<iomanip>输出浮点数的精度；
#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
    double a,b;
    cin>>a>>b;
    cout << "MEDIA = " << fixed << setprecision(5) <<  (a * 3.5 + b * 7.5 ) / 11 << endl;
    return 0;

}