import heapq
from collections import *
import math
def solve():
n, x, m = map(int, input().split())
maxi, mini = float("-inf"), float("inf")
x1, x2 = x, x
for i in range(m):
a, b = map(int, input().split())
f = 0
if (x1 >= a and x1 <= b) or (x2 >=a and x2<=b):
f = 1
maxi = max(maxi, a, b)
mini = min(mini, a, b)
if f == 1:
x1 = mini
x2 = maxi
if maxi - mini + 1 == float("-inf"):
print(1)
return
print(maxi - mini + 1)
t = int(input())
for _ in range(t):
solve()
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define mod 1000000007
#define ff first
#define se second
#define vc vector
ll bpow(ll a,ll b)
{
ll res=1;
while(b)
{
if(b&1)
{
res=res*a;
res%=mod;
}
a=a*a;
a%=mod;
b=b>>1;
}
return res;
}
ll fact(ll p)
{
ll ans=1;
for(ll i=1;i<=p;i++)
{
ans*=i;
ans%=mod;
}
return ans;
}
string num(ll n)
{
string res="";
while(n)
{
ll po=n%10;
n=n/10;
res+=to_string(po);
}
reverse(res.begin(),res.end());
return res;
}
int main()
{
int t;
cin>>t;
while(t--)
{
ll n,i,j,x,m;
cin>>n>>x>>m;
vector<pair<ll,ll>>v1(m);
for(i=0;i<m;i++)
{
ll l1,r1;
cin>>l1>>r1;
v1[i]={l1,r1};
}
ll curl=0,curr=0,op;
for(i=0;i<m;i++)
{
ll l2,r2;
l2=v1[i].ff;
r2=v1[i].se;
if(l2<=x and x<=r2)
{
curl=l2;
curr=r2;
op=i;
break;
}
}
if(curl!=0 and curr!=0)
{
for(i=op+1;i<m;i++)
{
ll l2,r2;
l2=v1[i].ff;
r2=v1[i].se;
if(l2>curr or r2<curl)
continue;
curl=min(curl,l2);
curr=max(curr,r2);
}
}
ll ans;
if(curl==0 and curr==0)
ans=1;
else
ans=curr-curl+1;
cout<<ans<<"\n";
}
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