I lived in berlin. I recommend going to romania, CodeForces rounds are right after school ends.

HappyNewYearGoodYear

Here is a seg tree:

#include <iostream>
#define int long long
using namespace std;
int aint[800005];
void update(int node, int st, int dr, int i, int val){
    if(st == dr){
        aint[node] = val;
        return;
    }
    int mid = (st+dr)/2;
    if(i <= mid)
        update(2*node+1, st, mid, i, val);
    else update(2*node+2, mid+1, dr, i, val);
    aint[node] = aint[2*node+1] + aint[2*node+2];
}
int query(int node, int st, int dr, int l, int r){
    if(st == l && dr == r){
        return aint[node];
    }
    int mid = (st+dr)/2, sum=0;
    if(l <= mid)
        sum += query(2*node+1, st, mid, l, min(r, mid));
    if(r > mid)
        sum += query(2*node+2, mid+1, dr, max(l, mid+1), r);
    return sum;
}
int32_t main(){
    int n, q;
    cin>>n>>q;
    for(int i=0; i<n; i++){
        int a;
        cin>>a;
        update(0, 0, n-1, i, a);
    }
    for(int i=0; i<q; i++){
        int cer, a, b;
        cin>>cer>>a>>b;
        if(cer == 1)
            update(0, 0, n-1, a-1, b);
        else cout<<query(0, 0, n-1, a-1, b-1)<<endl;
    }
}

I've just realised there might be a great chance I've been trolled

This you?