C

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int MAX = 200+10;
 4 int H[MAX];
 5 double dp[MAX][MAX];
 6 double get_dis(int a,int b) {
 7     return sqrt((double)a*(double)a+(double)b*(double)b);
 8 }
 9 int main() {
10     freopen("in1.txt","r",stdin);
11     freopen("out1.txt","w",stdout);
12     int n,w;
13     while(scanf("%d %d",&n,&w)==2) {
14         for(int i=0;i<n;i++) {
15             scanf("%d",&H[i]);
16         }
17         memset(dp,0,sizeof(dp));
18         for(int i=1;i<n;i++) {
19             for(int j=1;j<=H[i];j++) {
20                 for(int k=1;k<=H[i-1];k++) {
21                     dp[i][j]=max(dp[i][j],dp[i-1][k]+get_dis(w,abs(k-j)));
22                 }
23             }
24         }
25         double res=-1;
26         for(int i=1;i<=H[n-1];i++) {
27             res=max(res,dp[n-1][i]);
28         }
29         printf("%.3lf\n",res);
30     }
31 }