#include <iostream>
#include <cmath>
using namespace std;
#define PI 3.14159265

int main() {
	double a, b, alpha, h=0;
    cin >> a >> b >> alpha;
    h = ((a-b) / 2 ) * tan(alpha);
    cout << h * ( (a+b) / 2);
    return 0;
    }