#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,b,n=1; cin>>b; for(i=2;i<=b;i++){ if(i%2==1){ n-=i; } else{ n+=i; } } cout<<n; return 0; }