#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

int main(){
    int k;
    cin>>k;
    vector<int> line1;
    vector<int> line2;
    vector<int> sum;
    while(k--){
        int m,n;
        cin>>m>>n;
        line1.push_back(m);
        line2.push_back(n);
    }
    bool plus_1=false;
    for(int i=line1.size()-1;i>=0;i--){
        int temp=line1[i]+line2[i];
        if(plus_1){
            temp++;
        }
        if(temp>=10){
            plus_1=true;
            temp-=10;
        }else{
            plus_1=false;
        }
        sum.push_back(temp);

    }
    for(vector<int>::reverse_iterator iter=sum.rbegin();iter!=sum.rend();++iter){
        cout<<*iter;
    }
return 0;
}