#include<bits/stdc++.h>
using namespace std;
int main(){
    int z=1,n,a=1;
    cin>>n;
    while(z<=n){
        a=a+z;
        z=z+2;
    }
    cout<<a-1;
     
}
/**************************************************************
	Problem: 1003
	User: zhangyilei
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/