P1516 青蛙的约会

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

ll extend_gcd(ll a,ll b,ll &x,ll &y) {
	if (b == 0) {
		x = 1; y = 0; return a;
	}
	ll gcd = extend_gcd(b, a%b, y, x);
	y -= (a/b) * x;
	return gcd;
}

int main() {
	ll x, y, m, n, L; cin >> x >> y >> m >> n >> L;
	ll x0, y0, A = n-m, C = x-y;
	if (A < 0) { A = -A; C = -C;}
	ll gcd = extend_gcd(A, L, x0, y0);
	if (C % gcd == 0) {
		ll ans = (x0*C/gcd % (L/gcd) + L/gcd) % (L/gcd);
		cout << ans << endl;
	} else {
		cout << "Impossible" << endl; 
	}
	return 0;
}