poj 1061 青蛙的约会

#include<iostream>
#include<stdio.h>
using namespace std;
 long long  ext_gcd(long long a, long long  b, long long  *x, long long *y)
 {
     if(b==0)
     {
         *x = 1,*y = 0;
         return a;
     }
     else
     {
         long long  r = ext_gcd(b, a%b, x, y);
         long long  t = *x;
         *x = *y;
         *y = t - a/b * *y;
         return r;
     }
 }
int main()
{
    long long x,y,m,n,l;
    while(~scanf("%I64d%I64d%I64d%I64d%I64d",&x,&y,&m,&n,&l))
    {
        long long gcd_x,gcd_y;
        long long gcd = ext_gcd(n-m,l,&gcd_x,&gcd_y);
        if((x-y)%gcd)
        {
            printf("Impossible\n");
            continue;
        }
        long long ans= gcd_x*(x-y)/gcd;
        ans=(ans%(l/gcd)+(l/gcd))%(l/gcd);
       // cout<<(l/gcd)<<endl;
        printf("%I64d\n",ans);
    }
    return 0;
}