#include <stdio.h>

#define uint long long int

uint fn(uint a,uint b,uint c,uint * x,uint * y,uint * d)
{
	uint q,r,t,u;
	if(b==0)
	{
		if(a==0)
		{
			if(c)return 0;
			*x=*y=0;
			*d=0;
			return 1;
		}
		if(c%a)
		{
			return 0;
		}
		else
		{
			*x=c/a;
			*d=abs(a);
			*y=0;
			return 1;
		}
	}
	else
	{
		q=a/b;
		r=a-q*b;
		if(fn(b,r,c,&t,&u,d))
		{
			*x=u;
			*y=t-q*u;
			return 1;
		}
		else return 0;
		
	}
}

uint F(uint a,uint b,uint l)
{
	uint x,y,d,N,t,dx,dy;
	if(fn(b,-l,a,&x,&y,&d))
	{
		N=b/d*l;
		dx=N/b;
		dy=N/l;
		t=x/dx+1;
		x-=t*dx;
		y-=t*dy;
		t=y/dy+1;
		x-=t*dx;
		y-=t*dy;
		
		t=(-x-1)/dx+1;
		x+=t*dx;
		y+=t*dy;
		if(y<0)
		{
			t=(-y-1)/dy+1;
			x+=t*dx;
			y+=t*dy;
		}
		
		return x;
	}
	else return -1;
}

void solve(uint b, uint a, uint l)
{
	uint x;
	if(a==0)
	{
		printf("0\n");
		return;
	}
	if(b==0)
	{
		printf("FOREVER\n");
		return;
	}
	x=F(a,b,l);
	if(x==-1)
	{
		printf("FOREVER\n");
	}
	else
	{
		printf("%lld\n",x);
	}
}


int main(void)
{
	uint k, a, b, c, l;
	while(scanf("%lld %lld %lld %lld ", &a, &b, &c, &k), k||a||b||c)
	{
	  l=1<<k;
	  solve(c, (b-a+l)%l, l);
	}

	return 0;
}