#include <cstdio>
#include <algorithm>

typedef long long ll;

int main(){
    ll N;
    scanf("%lld", &N);

    ll res = 0;
    for(ll x=0;x<=N;x++){
        res = std::max(res, (x+1)*(N-x+1)-1);
    }

    printf("%lld\n", res);
}