/*
formula is : (base1 + base2) / 2 * height
*/
#include <stdio.h>
int main()
{
double base1, base2, height, area;
scanf("%lf %lf %lf", &base1, &base2, &height);
area = (base1 + base2) / 2 * height; // applying formula
printf("Area: %0.3lf
", area);
return 0;
}