代码如下

#include<bits/stdc++.h>
using namespace std;
int main(){
      int day , num = 0 , cnt = 0;
      cin >> day;
      for(int i = 1;i <= day;i++){
            for(int j = 1;j <= i;j++){
                  num += i;
                  cnt++;
            }
            if(cnt == day){
                  break;
            }
      }
      cout << num;
      return 0;
}