#include<bits/stdc++.h>
using namespace std;
int main(){
	int n=1,h=0;
	while(n<=100){
		h=h+n;
		n+=3;
	}
	cout<<h;
	
}
/**************************************************************
	Problem: 1053
	User: hongjiaming
	Language: C++
	Result: Accepted
	Time:4 ms
	Memory:2072 kb
****************************************************************/