这里需要注意商家不是倒贴；最多免费。 
int main()
{
    int mon,day,cou;
    float price=0;
    scanf("%f %d %d %d",&price,&mon,&day,&cou);
    if(mon==11&&day==11)
    {
        if(cou==1)
        printf("%0.2lf",(0.7*price-50.00>=0?0.7*price-50.00:0));
        else
        printf("%0.2lf\n",price*0.7);
    }
    else
    {
        if(mon==12&&day==12)
    {
        if(cou==1)
        {
        printf("%.2lf\n",(price*0.8-50>=0?price*0.8-50:0));
        }
        else
        printf("%.2lf\n",price*0.8);
    }
    }

    
    return 0;
}