#include <stdio.h>#include <algorithm>using namespace std;struct rectangle{int x;int y;}r[1008];int cmp(const rectangle &a, const rectangle &b){if(a.y != b.y){return a.y >b.y;}else{return a.x > b.x;}}void solve(){int t;int x;int y;int sum;while(scanf("%d",&t)!=EOF){sum = 0;if(t == -1){break;}memset(r,0,sizeof(r));for(int i = 0 ;i < t; i++){scanf("%d%d",&r[i].x,&r[i].y);if(r[i].x > r[i].y){swap(r[i].x,r[i].y);}}sort(r,r+t,cmp);int dx = min(r[0].x,r[1].y);int dy = min(r[1].x,r[0].y);sum = dx*dy+(r[1].y-dx)*dy+(r[0].y - dy)*dx;for(int i = 2; i< t ;i ++){if(r[i].x > dx && r[i].y >dy){sum+=(r[i].x-dx)*(r[i].y-dy);dx = r[i].x;}else if(r[i].x > dy && r[i].y >dx){sum+=(r[i].x-dy)*(r[i].y-dx);dy = r[i].x;}}printf("%dn",sum);}}int main(){solve();return 0;}
