#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;
 
int main() {
    int n;
    cin >> n;
    unordered_map<int, int> suma_Produktow;
    vector<int> kolejnosc;
    for (int i = 0; i < n; ++i) {
        int A, K;
        cin >> A >> K;
        if (suma_Produktow.find(A) == suma_Produktow.end()) {
            kolejnosc.push_back(A);
        }
        suma_Produktow[A] += K;
    }
    cout << kolejnosc.size() << "\n";
    for (int a : kolejnosc) {
        cout << a << " " << suma_Produktow[a] << "\n";
    }
    return 0;
}

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6
2 1
3 11
1 4
3 2
7 1
2 1