#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
long long x1[101],y1[101],x[201],x2[101],y2[101],y[201];
int n;
int main()
{scanf("%d",&n);for (int i=1;i<=n;i++){scanf("%lld%lld%lld%lld",&x1[i],&y1[i],&x2[i],&y2[i]);x[i*2-1]=x1[i];x[i*2]=x2[i];y[i*2-1]=y1[i];y[i*2]=y2[i];}sort(x+1,x+2*n+1);sort(y+1,y+2*n+1);long long ans=0;for (int i=2;i<=2*n;i++)for(int j=2;j<=2*n;j++) { long long s=(long long)(x[i]-x[i-1])*(long long)(y[j]-y[j-1]);for (int k=1;k<=n;k++) if (x[i-1]>=x1[k]&&y[j-1]>=y1[k]&&x[i]<=x2[k]&&y[j]<=y2[k]){ ans=(long long)ans+s;break; }} printf("%lld",ans); return 0;
}