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#include<iostream>
using namespace std;
int main(){
	int a,b,c,day,coin;
	cin>>a;
	day=0;
	coin=0;
	for(b=1;;b++){
		for(c=1;c<=b;c++){
			if(day>a){
				cout<<coin;
				return 0;
			}else{
				coin+=c;
				day++;
			}
		}
	}
}