#include <iostream>

 #include<cstdio>

 #include<cstring>

 #include<algorithm>

 #include<stdlib.h>

 using namespace std;

 #define INF 0xfffffff

 int ca[][],dp[][];

 int main()

 {

     int t,g,i,j,k,n,s,d;

     cin>>t;

     while(t--)

     {

         cin>>n>>k>>d>>s;

         memset(ca,,sizeof(ca));

         for(i = ; i <= k ;i++)

         scanf("%d%d",&ca[i][],&ca[i][]);

         for(i =  ; i <= k ; i++)

             for(j =  ; j <= n ;j++)

             dp[i][j] = INF;

         if(n==)

         {

             printf("0\n");

             continue;

         }

         if(ca[][]>=n)

         {

             cout<<d+ca[][]*n<<endl;

             continue;

         }

         for(i = n-ca[][] ; i < n ; i++)

         dp[][i] = n*ca[][]+d;

         dp[][n] = n*ca[][];

         for(i = ; i <= k ;i++)

         {

             for(j = ; j <= n ; j++)

             {

                 dp[i][j] = dp[i-][j]+j*(ca[i][]-ca[i-][]);

                 for(g = j+ ; g <= j+ca[i][]&&g <= n  ;g++)

                 dp[i][j] = min(dp[i][j],dp[i-][g]+g*(ca[i][]-ca[i-][])+d);

             }

         }

         if(dp[k][]==INF)

         puts("impossible");

         else

         cout<<dp[k][]<<endl;

     }

     return ;

 }