解（if有点慢，还是用switch吧）

#include<iostream>
using namespace std;
int main(){
int n;
cin>>n;
switch(n%7){
case 0:cout<<"monday";break;
case 1:cout<<"tuesday";break;
case 2:cout<<"wednesday";break;
case 3:cout<<"thursday";break;
case 4:cout<<"friday";break;
case 5:cout<<"saturday";break;
default:cout<<"sunday";
}
return 0;
}