题解

#include <iostream>
using namespace std;
int main(){
    int k, n=1, count=1, sum=0;
    cin>>k;
    for(int i=1; i<=k; i++){
        sum+=n;
        if(n==count){
            n++;
            count=1;
            continue;
        }
        count++;
    }
    cout<<sum<<endl;
    return 0;
}