暴力枚举即可

#include<bits/stdc++.h> 
using namespace std; 
int main(){
    int n;
    cin>>n;
    int m=n+1;
    if(m%7==1)cout<<"monday";
    if(m%7==2)cout<<"tuesday";
    if(m%7==3)cout<<"wednesday";
    if(m%7==4)cout<<"thursday";
    if(m%7==5)cout<<"friday";
    if(m%7==6)cout<<"saturday";
    if(m%7==0)cout<<"sunday";
	return 0;
}