BZOJ 1477: 青蛙的约会

二次联通门 : BZOJ 1477: 青蛙的约会

/*
    BZOJ 1477: 青蛙的约会

    扩展欧几里得
    列出方程, 判断一下
*/
#include <iostream>
#include <cstdio>
typedef long long LL;
#define rg register
void read (LL &n)
{
    rg char c = getchar ();
    for (n = 0; !isdigit (c); c = getchar ());
    for (; isdigit (c); n = n * 10 + c - '0', c = getchar ());
}
LL Extend_Euclid (LL a, LL b, LL &x, LL &y)
{
    if (!b) { x = 1, y = 0; return a; }
    LL now = Extend_Euclid (b, a % b, x, y);
    LL res = x; x = y, y = res - a / b * y; return now;
}
LL N, M, Length, X, Y;
int main (int argc, char *argv[])
{
    read (X), read (Y), read (M), read (N), read (Length);
    LL now_1, now_2, now = Extend_Euclid ((N - M), Length, now_1, now_2);
    LL R = Length / now;
    if ((X - Y) % now) printf ("Impossible");
    else printf ("%lld", ((X - Y) / now * now_1 % R + R) % R); return 0;
}