#include <stdio.h>
int main() {
   signed long vys[65535];
   unsigned k,i,p;
   unsigned long a,b,c,max;
   signed long variable;
   scanf("%li %li %li %d", &a, &b, &c, &k);
   p = 0;
   while((a!=0) && (b!=0) && (c!=0) && (k!=0)) {
      p++;
      max=1;
      for (i=1;i<=k;i++) max=max*2;
      variable=b-a;
      if (variable < 0) variable += max;
      if (variable %c!=0) vys[p]=-1;
      else vys[p] = variable/c;
      scanf("%li %li %li %d", &a, &b, &c, &k);
   }
   for (a=1;a<=p;a++) if (vys[a]==-1) printf("FOREVER\n");
      else printf("%li\n",vys[a]);
   return (0);
}