poj1061 2010.2.17

poj1061 2010.2.17

#include <iostream>
using namespace std;
__int64 x,y,m,n,l;
__int64 modularLinearEquation(__int64 a,__int64 b,__int64 n);
__int64 extEuclid(__int64 a, __int64 b);
int main(void)
{
	__int64 s;
	scanf("%I64d",&x);
	scanf("%I64d",&y);
	scanf("%I64d",&m);
	scanf("%I64d",&n);
	scanf("%I64d",&l);
	s=modularLinearEquation((n-m+l)%l,(x-y+l)%l,l);
	if (s<0)
		printf("Impossible\n");
	else
		printf("%I64d\n",s);
	return 0;
}
__int64 modularLinearEquation(__int64 a,__int64 b,__int64 n)
{
	__int64 d,result;
	result=-1;
	d=extEuclid(a,n);
	if (b%d!=0) return result;
	x=x*(b/d);
	x=(x%(n/d)+n/d)%(n/d);
	result=x;
	return result;
}
__int64 extEuclid(__int64 a, __int64 b)
{
	__int64 r,t;
    if (b==0)
	{  
		x=1;
		y=0;
		return a;
	}
    r=extEuclid(b,a%b);
	t=x;      
	x=y; 
	y=t-a/b*y;
    return r;
}