题解 | #求 1 - n 之间偶数的和#

#include <iostream>
using namespace std;

int main() {
    
    int n;
    cin >> n;
    int sum = 0;
    
    // write your code here......
    if(n%2!=0) --n;
    sum = (2+n)/2*n/2;

    cout << sum << endl;
    
    return 0;
}