#include<iostream>

using namespace std;
const int N=110;
int p[N][N];
int n;
int main(){
    cin>>n;
    while(n--){
        int x1,y1,x2,y2;
        scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
        x1++,y1++;
        p[x1][y1]+=1;
        p[x2+1][y1]-=1;
        p[x1][y2+1]-=1;
        p[x2+1][y2+1]+=1;
    }
    int ans=0;
    for(int i=1;i<=101;i++)
        for(int j=1;j<=101;j++){
            p[i][j]+=p[i-1][j]+p[i][j-1]-p[i-1][j-1];
            if(p[i][j]) ans++;
        }
    cout<<ans;
    return 0;
}