(^_^)

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