1001 Sum Problem

#include<iostream>#include<algorithm>using namespace std;int main(){    long long a;    while(cin>> a){        if(a%2 == 0) cout << a/2 * (a+1) << "\n\n";        else cout << (a+1)/2 *a << "\n\n";    }    return 0;}

这种题考的就是范围