三分模板

double solve()
{
    double M,RM;
    double L = 0.0;
    double R = INF;
    while (L + eps < R)
    {
        M = (L + R) / 2;
        RM = (M + R) / 2;
        if (calc(M) < calc(RM))
            R = RM;
        else
            L = M;
    }
    return R;
}