#include<iostream>
using namespace std;
int main(){
	int n,a[5][3003],ans[3003];
	ans[0]=0;
	cin>>n;
	for(int i=1;i<=n;i++){
		int x;
		cin>>a[1][i]>>a[2][i];
		x=a[1][i]+a[2][i]-8;
		ans[i]=ans[i-1]+x;
	}
	cout<<ans[n];
	return 0;
}```