1 #include <iostream>
 2 #include <cstdio>
 3 using namespace std;
 4 
 5 int main()
 6 {
 7     int n, n1, n2, sum;
 8     while (scanf("%d",&n) != EOF)
 9     {
10         sum = 0;
11         if(n%2 == 0)
12         {
13             n1 = n/2;
14             n2 = n/2;
15         }
16         else
17         {    
18             n1 = n/2;
19             n2 = n-n1;
20         }
21         sum = n1*(n1-1)/2 + n2*(n2-1)/2;
22         printf("%d\n",sum);
23     }
24     return 0;
25 }