C :

#include <stdio.h>

void main(){
	int a,b,c,t;
	double s;
	scanf("%d%d%d",&a,&b,&c);
	
	if(a > b){
		t=a;a=b;b=t;
	}
	
	if(b > c){
		t=b;b=c;c=t;
	}
	
	if(a*a+b*b==c*c){
		s = a * b / 2.0;
		printf("%.1f",s); 
	}else{
		printf("No"); 
	}
}

C++ :

#include<iostream>
#include <iomanip>
using namespace std;
int main(){
	int a,b,c,t;
	double s;//面积
	cin>>a>>b>>c;
	if(a>b){
		t=a;
		a=b;
		b=t;
		
	}
	if(b>c){
		t=b;
		b=c;
		c=t;
	}

	
	if(a*a+b*b==c*c){
		s = a * b * 1.0 / 2;
		cout<<fixed<<setprecision(1)<<s<<endl;
		
	}else{
		cout<<"No"<<endl;
	}
}

Python :

a,b,c=map(int,input().split(" "))
if a**2+b**2==c**2:
    s=0.5*a*b
    print("%.1f"%s)
elif a**2+c**2==b**2:
    s=0.5*a*c
    print("%.1f"%s)
elif b**2+c**2==a**2:
    s=0.5*b*c
    print("%.1f"%s)
else:
    print("No")