#include<iostream>
using namespace std;

int main(){
	int s=0;
	for	(int i=100;i>=1;i-3){
		s=s+i;
	}
	cout<<s;
	return 0;
}
/**************************************************************
	Problem: 1053
	User: linweilun
	Language: C++
	Result: Time Limit Exceed
****************************************************************/