Platforms

Platforms

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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 exactlyd 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.

Input

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].

Output

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.

Sample test(s) input

2 2 5 3

output

4

input

5 4 11 8

output

20

题目大意：

在数轴上，步长为D，如果跳到某个平台的右边而且在下一个平台之间左边的缝里，那就掉下去了，就是输出掉下去的坐标了。但是交了不少遍，老是WA，不知为何。。第二天网络流畅了看了看标程，原来int放不下，虽然有说台子不会超过10^6,但是处理蹦跶的步数的时候却有几率超过10^10的边界，6*2=12>10嘛。。。。看来要认真点了。

#include <iostream>
using namespace std;
int main()
{long long n,d,m,l;long long step;while(cin>>n>>d>>m>>l){long long min,max;for(int i=0;i<n;i++){min=i*m+l;//第i个平台右边的边界max=(i+1)*m;//第i+1个平台左边的边界step=(min+d)/d;if(step*d<max)break;}cout<<step*d<<endl;}return 0;
}