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){
        sum=0;
    }
    else{
        for (int i=2;i<=n;i++){
            sum+=i;
            i++;
        }
    }
    cout << sum << endl;
    
    return 0;
}