CF18B.Platforms

In one one-dimensional world there are n platforms. Platform with index k (platforms are numbered from 1) is a segment with coordinates [(k - 1)m, (k - 1)m + l], and l < m. Grasshopper Bob starts to jump along the platforms from point 0, with each jump he moves exactly d units right. Find out the coordinate of the point, where Bob will fall down. The grasshopper falls down, if he finds himself not on the platform, but if he finds himself on the edge of the platform, he doesn't fall down.

在一维世界中有 $n$ 个平台。编号为 $k$ 的平台（平台编号从 1 开始）是一条线段，其坐标范围为 $[(k - 1)m, (k - 1)m + l]$，且满足 $l < m$。蚱蜢 Bob 从坐标 0 出发，沿平台向右跳跃，每次跳跃恰好移动 $d$ 个单位长度。请找出 Bob 最终坠落位置的坐标。当 Bob 所处位置不在任何平台上时，他就会坠落；但如果他恰好落在某个平台的边缘上，则不会坠落。

The first input line contains 4 integer numbers n, d, m, l (1 ≤ n, d, m, l ≤ 106, l < m) — respectively: amount of platforms, length of the grasshopper Bob's jump, and numbers m and l needed to find coordinates of the k-th platform: [(k - 1)m, (k - 1)m + l].

第一行输入包含 4 个整数 $n$、$d$、$m$、$l$（$1 ≤ n, d, m, l ≤ 10^6$，且 $l < m$），分别表示平台的数量、蚱蜢 Bob 的跳跃长度，以及用于计算第 $k$ 个平台坐标的两个数 $m$ 和 $l$：其坐标区间为 [(k - 1)m, (k - 1)m + l]。

Output the coordinates of the point, where the grosshopper will fall down. Don't forget that if Bob finds himself on the platform edge, he doesn't fall down.

输出蚱蜢最终掉落点的坐标。请注意，如果鲍勃恰好位于平台边缘，则他不会掉落。