#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
typedef long long ll;
int n;
map<ll, ll>h;
int xb[N];
// priority_queue<int, vector<int>, greater<int>>heap;
// set<ll>st;
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for(int i = 1;i <= n;i++){
        int x, y;
        cin >> x >> y;
        h[x] += y;
    }

    int ans = 0;
    for(auto &[a, b] : h){
        if(h[a] > 1){
            h[2 * a] += b / 2;
            h[a] %= 2;
        }
        ans += h[a];
    }

    cout << ans << endl;
    return 0;
}