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#include <iostream>

using namespace std;

typedef long long ll;

int main(){ // DAYXICH
    freopen("DAYXICH.INP","r",stdin);
    freopen("DAYXICH.OUT","w",stdout);

    short d, r; ll n;
    cin >> d >> r >> n;
    cout << 2*d + 2*r*n << endl;
    
    return 0;
}