import std;

void main () {
    int W, Z;
    double B;
    readln.read(W, Z, B);

    int ans = cast(int) ((W+Z) * (B+1));
    writeln(ans);
}

void read(T...)(string S, ref T args) {
    auto buf = S.split;
    foreach (i, ref arg; args) {
        arg = buf[i].to!(typeof(arg));
    }
}