#include<iostream>
using namespace std;
int main()
{
    int n,m,k,a[3000],b[3000];
    k=0;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        cin>>a[i]>>b[i];
        m=a[i]+b[i]+k-8;
        k=k+m;
    }
    
    cout<<k;
}