40分，c++求助

#include<iostream>
using namespace std;
int main(){
    long long k,coin=0,day=1;
    cin>>k;
    for(long long n=1;n<=k;n++){
        for(long long i=1;i<=n;i++){
            coin+=n;
            day++;
        }
        if(day>k) break;
    }
    cout<<coin;
    return 0;
}