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

/**************************************************************
	Problem: 1053
	User: zhengzihao3
	Language: C++
	Result: Wrong Answer
****************************************************************/