#include<bits/stdc++.h>
using namespace std;
int main()
{
	int i,s=0;
	for(i=100;i>=1;i-=3){
		s+=i;
		
		
	}
	cout<<s;
	
	


	return 0;
}

/**************************************************************
	Problem: 1053
	User: zy002
	Language: C++
	Result: Accepted
	Time:4 ms
	Memory:2072 kb
****************************************************************/