#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <cstring>
#include <queue>
#include <string>
#include <map>
#include <stack>
#include <list>
#include <set>
 
using namespace std;
 
int main()
{
    int t,n,x,y,cnt,in;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        in = cnt = 0;
        for(int i = 0; i < n; i++)
        {
            scanf("%d%d",&x,&y);
            in += x;
            if(in < y)
            {
                cnt += (y-in);
                in += (y-in);
            }
            in -= y;
        }
        printf("%d\n",cnt);
    }
    return 0;
}