poj 1061 青蛙的约会

http://poj.org/problem?id=1061

#include<iostream>

#include<cstdio>

#include<algorithm>

#include<cstring>

#include<cmath>

#include<map>

#include<queue>

#include<cmath>

#define LL long long



using namespace std;



LL gcd(LL x,LL y)

{

    if(x%y==0)

    return y;

    return gcd(y,x%y);

}

void exgcd(LL a,LL b,LL *x,LL *y)

{

    if(b==0)

    {

        *x=1;

        *y=0;

        return ;

    }

    exgcd(b,a%b,x,y);

    LL t=*x;

    *x=*y;

    *y=(t-(a/b)*(*y));

}

int main()

{

   LL x,y,m,n,L;

   while(cin>>x>>y>>m>>n>>L){

   if(m==n)

   {

       printf("Impossible\n");

       continue;

   }

   LL a=n-m;

   LL b=x-y;

   LL k=gcd(L,a);

   if(b%k!=0)

   {

       printf("Impossible\n");

   }else

   {

       LL x1,y1;

       L/=k;

       a/=k;

       b/=k;

       exgcd(L,a,&x1,&y1);

       y1*=b;

       y1=(y1%L+L)%L;

       cout<<y1<<endl;

   }

   }

   return 0;

}