#include <iostream>

#include <cstdio>

#include <algorithm>

using namespace std;

const int inf=(1<<25);

int dp[105][105];

struct Car{

	int ti,zi;

}cars[110];

int main(){

	int T,n,k,d,s,cnt,t,z;

	scanf("%d",&T);

	while(T--){

		scanf("%d%d%d%d",&n,&k,&d,&s);

		cnt=0;

		for(int i=1;i<=k;i++){

			scanf("%d%d",&t,&z);

			if(t<=s){

				cnt++;

				cars[cnt].ti=t; cars[cnt].zi=z;

			}

		}

		for(int i=0;i<=n;i++)

		for(int j=0;j<=cnt;j++) dp[i][j]=inf;

		dp[n][0]=0;

		for(int j=1;j<=cnt;j++){

			for(int i=0;i<=n;i++){

				if(i==0){

					dp[i][j]=dp[i][j-1];

					for(k=1;k<=cars[j].zi;k++){

						if(i+k>n) break;

						dp[i][j]=min(dp[i][j],dp[i+k][j-1]+k*(cars[j].ti-cars[j-1].ti)+d);

					}

				}

				else{

					dp[i][j]=dp[i][j-1]+i*(cars[j].ti-cars[j-1].ti);

					for(k=1;k<=cars[j].zi;k++){

						if(k+i>n) break;

						dp[i][j]=min(dp[i][j],dp[i+k][j-1]+(i+k)*(cars[j].ti-cars[j-1].ti)+d);

					}

				}

			}

		}

		int ans=inf;

		for(int i=0;i<=cnt;i++){

			ans=min(ans,dp[0][i]);

		}

		if(ans!=inf) printf("%d\n",ans);

		else puts("impossible");

	}

	return 0;

}