#include <iostream>
#include <math.h>

using namespace std;

int main() {
	int a,b,c;
	float r,s,p;
	cout<<"Nhap do dai 3 canh a,b,c: "; cin>>a>>b>>c;
	p = (a + b + c) / 2;
	s = sqrt(p * (p - a) * (p - b) * (p - c));
	r = (a * b * c) / (4 * s);
	cout<<"Ban kinh duong tron ngoai tiep R = "<<r;
	return 0;
}