题解 | #求 1 - n 之间偶数的和#

using namespace std;

int main() {
    
    int n;
    cin >> n;
    int sum = 0;
    int i;
    for(i=1;i<=n;i++){
        if(i%2==0){
            sum+=i;
        }
    }
    
    // write your code here......
    

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