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

/**************************************************************
	Problem: 1053
	User: zhuangsongyu
	Language: C++
	Result: Accepted
	Time:5 ms
	Memory:2072 kb
****************************************************************/