#include <iostream>
#include <iomanip>
#include<cmath>
using namespace std;
int main()
{
/* double r;
double pi = 3.141592653;
cin >> r;
cout << fixed << setprecision(9) << (pi * r * r);
*/
// long long x;
// long long y;
// int a , b;
// cin >> x >> y;
// a = x % 10;
// b = y % 10;
// cout << a + b;
/* long long x, y, n;
cin >> n >> x >> y;
cout << n * (y - x) << endl;
*/
/*long long x, y;
cin >> x >> y;
cout << x / y;
*/
/* cout << fixed << setprecision(6);
double n, r;
double pi = 3.141592;
cin >> n >> r;
cout << fixed << setprecision(6) << (pi * r * r) - (n * n);
*/
/*double x, y;
cin >> x >> y;
long long ans = ceil(x / y);
cout << ans;
*/
/*long long n;
cin >> n;
cout << 0 << " " << 0;
*/
/*double a, b;
cin >> a >> b;
cout << "floor " << a << " / " << b << " = " << floor(a / b) << endl;
cout << "ceil " << a << " / " << b << " = " << ceil(a / b) << endl;
cout << "round " << a << " / " << b << " = " << round(a / b) << endl;
*/
/* long long n, sum;
cin >> n;
sum = (n * (n + 1)) / 2;
cout << sum; */
double a, b, c;
cin >> a >> b >> c;
cout << fixed << setprecision(6) << 2*a*c+3*b*c;
/* long long n;
cin >> n;
cout << n;
*/
/* double r;
double pi = 3.141592;
cin >> r;
cout << fixed << setprecision(4) << (pi * r * r) + (0.5 * 2 * r * 1.732050 * r) - (0.5 * r * 60);
*/
return 0;
}
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