#include<iostream>
#include<vector>
using namespace std;
class BinTree:vector<int>
{
public:
explicit BinTree(int k=0)
{
assign(k+1,0);
}
int lowbit(int k)
{
return k&-k;
}
int sum(int k)
{
return k>0?sum(k-lowbit(k))+(*this)[k]:0;
}
int last()
{
return size()-1;
}
void add(int k,int w)
{
if(k>last())return;
(*this)[k]+=w;
add(k+lowbit(k),w);
}
};
int main()
{
BinTree test(123);
test.add(27,72);
cout<<test.sum(26)<<' '<<test.sum(27)<<' '<<test.sum(123);
}