bzoj 2306

%%%%http://blog.csdn.net/popoqqq/article/details/43926365

 #include<bits/stdc++.h>
 #define INF 0x7fffffff
 #define LL long long
 #define N 100005
 using namespace std;
 inline int ra()
 {
     int x=,f=; char ch=getchar();
     while (ch<'' || ch>'') {if (ch=='-') f=-; ch=getchar();}
     while (ch>='' && ch<='') {x=x*+ch-''; ch=getchar();}
     return x*f;
 }
 double p,ans,a[],f[][],g[][];
 int main()
 {
     int n=ra(),m=ra();
     for (int i=; i<=n; i++)
         scanf("%lf",&a[i]);
     int st=ra();
     scanf("%lf",&p);
     memset(f,0xc2,sizeof(f));
     for (int i=; i<=n; i++)
         f[i][i]=;
     for (int i=; i<=m; i++)
     {
         int x=ra(),y=ra();
         f[x][y]=a[y];
     }
     double tmp=p;
     for (int T=; T<=; T++,tmp*=tmp)
     {
         memset(g,0xc2,sizeof(g));
         for (int k=; k<=n; k++)
             for (int i=; i<=n; i++)
                 for (int j=; j<=n; j++)
                     g[i][j]=max(g[i][j],f[i][k]+f[k][j]*tmp);
         memcpy(f,g,sizeof(f));
     }
     for (int i=; i<=n; i++)
         ans=max(ans,f[st][i]);
     printf("%.1lf\n",ans*p+a[st]);
     return ;
 }