#include <bits/stdc++.h>
using namespace std;
int ans;
int n;
int a[3005],b[3005];
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i]>>b[i];
		ans=ans+(a[i]+b[i]-8);
	}
	cout<<ans<<endl;
	return 0;
}