// 11493

#include <stdio.h>
#include <iostream.h>

int min(int a, int b){
  return (a<b ? a : b);
}

int calculate(int count[10001], int N, int M, int L) {
  if (100*N % L==0) {
    int rows = 100*N/L;
    int fullplanks = min(rows,count[M]);
    int twoplanks = rows-fullplanks;
    int avail = (M%2==0 ? count[M/2]/2 : 0);
    for (int i=1; i<=(M-1)/2; i++)
      avail += min(count[i],count[M-i]);
    if (avail >= twoplanks) 
      return fullplanks+2*twoplanks;
    else 
      return -1;
  }
  else return -1;
}

int main(){
  int N,M;
  cin >> N;
  cin >> M;
  while (N>0) {
    int L, K;
    cin >> L;
    cin >> K;
    int count[10001] = {0};
    for (int i=0; i<K; i++){
      int x;
      cin >> x;
      count[x]++;
    }
    int method1 = calculate(count,N,M,L);
    int method2 = calculate(count,M,N,L);
    if (method1==-1 && method2==-1) cout << "impossivel\n";
    else if (method1==-1) cout << method2 << "\n";
    else if (method2==-1) cout << method1 << "\n";
    else cout << min(method1,method2) << "\n";
    cin >> N;
    cin >> M;
  }
}