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