题解

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    double m,n;
    cin>>m>>n;
    printf("%.10f",(m*m+n*n)-((m+n)*m/2+n*n/2));
    return 0;
}

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    double m,n;
    cin>>m>>n;
    printf("%.10f",m*m/2+n*(n-m)/2);
    return 0;
}