#include <iostream>
using namespace std;

void tong()
{
	int n;
	float s=0;
	cout<<"Nhap n: ";cin>>n;
	for(int i=1;i<=n;i++)
	{
		float tmp = i*1.0*(i+1)/(i+2)/(i+3);
		s+=tmp;
	}
	cout<<"=> S = "<<s<<endl;
}

void ngay()
{
	int th,nam;
	do{
		cout<<"Nhap thang: ";cin>>th;
	}while(th>12 && th<1);
	do
	{
		cout<<"Nhap nam: ";cin>>nam;
	}while(nam<0);
	cout<<"Thang "<<th<<" nam "<<nam<<" co ";
	switch(th)
	{
		case 1:
		case 3:
		case 5:
		case 7:
		case 8:
		case 10:
		case 12:
		{
			cout<<"31 ngay\n";
			break;
		}
		case 4:
		case 6:
		case 9:
		case 11:
		{
			cout<<"30 ngay\n";
			break;
		}
		case 2:
		{
			if(nam%4==0)
				cout<<" 29 ngay\n";
			else
				cout<<" 28 ngay\n";
		}
	}
}

int main(int argc, char *argv[])
{
	int m;
	while(1)
	{
		do
		{
			system("cls");
			cout<<"1. Tinh tong S\n2. Tim so ngay cua thang/nam\n0. Thoat!!!\n\n\nNhap lua chon (0-2): ";
			cin>>m;
			switch(m)
			{
				case 1:
				{
					system("cls");
					tong();
					system("pause");
					break;
				}
				case 2:
				{
					system("cls");
					ngay();
					system("pause");
					break;
				}
				case 0:
				{
					system("cls");
					cout<<"Ket thuc!!!";
					return 0;
				}
			}
		}while(m>2 && m<0);
	}
	return 0;
}