编辑代码

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
#define lowbit(x) ((x)&(-x))
int tree[10000],n,a;
void add(int x,int d){
	while(x<=n){
		tree[x]+=d;
		x+=lowbit(x);
	}
}
int sum(int x){
	int su=0;
	while(x>0){
		su+=tree[x];
		x-=lowbit(x); 
	} 
	return su;
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a;
		add(i,a);
	}
	int m;
	cin>>m;
	cout<<sum(m);
	return 0;
}