#include<stdio.h>
#include<iostream.h>
#include<math.h>
int euclid(int a,int b)
{
   if (b==0) return a;
      else return(euclid(b,a%b));
   }
int ext_euclid(int a,int b,int &x,int &y)
{
   int t,d;
   if (b==0) {x=1;y=0;return a;}
   d=ext_euclid(b,a %b,x,y);
   t=x;
   x=y;
   y=t-a/b*y;
   return d;
}
void modular_linear_equation_solver(int a,int b,int n)
{
   int e,i,d;
   int x,y;
   int min,k;
   d=ext_euclid(a,n,x,y);
   if (b%d>0) cout <<"FOREVER\n";
      else
	  {     min=0xfffffff;
			e=(x*(b/d))%n;
            for (i=0;i<d;i++)  
			{  k=((e+i*(n/d))%n); 
				if (k>=0&&k<min)
					min=k;

			}
			cout <<min<<'\n';
            }
   }
int  main()
{   int a,b,c,d,i,m;
    while(1)
	{   
        cin>>a>>b>>c>>d;
		if(a==0&&b==0&&c==0&&d==0)
			break;
	    m=1;
	    if(d==0)
		     m=1;
	    else
		    for(i=1;i<=d;i++)
		      m*=2;   
		modular_linear_equation_solver(c,b-a,m);
	}
	return 0;
}

• 溢出了 (1078) tmpbt 2005-01-19 22:21:15