#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int i,a,sums=1; cin>>a; for(i=2;i<=a;i++){ if(i%2==0) sums+=i; else sums-=i; } cout<<sums; return 0; }