#include<bits/stdc++.h>
using namespace std;
int main(){
	int a=1,b=100,h=0;
	do{
		h=h+a;
		a+=3;
	}while(a<=b);
	cout<<h;

}
/**************************************************************
	Problem: 1053
	User: zhuangwenya
	Language: C++
	Result: Accepted
	Time:4 ms
	Memory:2072 kb
****************************************************************/