poj 1061 青蛙的约会（gcd拓展，解不定方程）

void ex_gcd(LL a, LL b, LL &d, LL &x, LL &y) {
if (!b) {d=a;x=1;y=0;}
else{
ex_gcd(b, a%b, d, y, x);y -= a/b*x;
}
}

int main() {
#ifndef ONLINE_JUDGE
freopen("input.in", "r", stdin);
//freopen("output.txt", "w", stdout);
#endif
SPEED_UP
cin >> x >> y >> m >> n >> L;
if (n == m) {cout << "Impossible\n";return 0;}

LL a = n - m, b = x - y, k, r, d;
ex_gcd(a, L, d, k, r);
if (b%d != 0) {
cout << "Impossible\n";
}
else {
L = L/d;
b = b/d;
k = (k*b%L+L)%L;
cout << k << endl;
}
return 0;
}