#include <bits/stdc++.h>
int main() {
  int n;
  int abc[4001];
  abc[0] = 1;
  abc[4000] = 1;
  for (int i = 2; i < 2001; i++) {
    abc[i - 1] = abc[i - 2] + i;
    abc[4000 - (i - 1)] = abc[i - 1];
  }
  while (scanf("%d", &n) != EOF) {
    int ans = 0;
    int is = n - 1000;
    if (is < 0) is = 0;
    for (int i = is; i < n + 1; i++) ans += abc[i];
    printf("%d\n", ans);
  }
  return 0;
}
