const int MAXN = (1 << 20) + 10;
int n, END;
int t[2*MAXN]; // or long long

void build (int v, int tl, int tr) {
    if (tl == tr)
        return;
    else {
        int tm = (tl + tr) / 2;
        build (v*2, tl, tm);
        build (v*2+1, tm+1, tr);
        t[v] = t[v*2] + t[v*2+1];
    }
}

int sum (int v, int tl, int tr, int l, int r) {
    if (l > r)
        return 0;
    if (l == tl && r == tr)
        return t[v];
    int tm = (tl + tr) / 2;
    return sum (v*2, tl, tm, l, min(r,tm))
        + sum (v*2+1, tm+1, tr, max(l,tm+1), r);
}

void update (int v, int tl, int tr, int pos, int new_val) {
    if (tl == tr)
        t[v] = new_val;
    else {
        int tm = (tl + tr) / 2;
        if (pos <= tm)
            update (v*2, tl, tm, pos, new_val);
        else
            update (v*2+1, tm+1, tr, pos, new_val);
        t[v] = t[v*2] + t[v*2+1];
    }
}

int main() {
    cin >> n;
    while (END < n) END <<= 1;
    for (int i = 0; i < n; i++) {
        cin >> t[END + i];
    }
    build();

    // using sum(1, 1, END, l, r)
    // using update(1, 1, END, pos, value)