bzoj 2134

水概率DP，ANS=sigma(min(a[i],a[i-1])/(a[i]*a[i-1]))

#include<bits/stdc++.h>
#define inc(i,l,r) for(int i=l;i<=r;i++)
#define dec(i,l,r) for(int i=l;i>=r;i--)
#define link(x) for(edge *j=h[x];j;j=j->next)
#define mem(a) memset(a,0,sizeof(a))
#define inf 1e9
#define ll long long
#define succ(x) (1<<x)
#define lowbit(x) (x&(-x))
#define NM 10000000+5
using namespace std;
int read(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
    while(isdigit(ch))x=x*10+ch-'0',ch=getchar();
    return x*f;
}
int n,A,B,C,a[NM];
double s;
int main(){
    freopen("data.in","r",stdin);
    scanf("%d%d%d%d%d",&n,&A,&B,&C,a+1);
    for (int i=2;i<=n;i++) a[i] = ((long long)a[i-1] * A + B) % 100000001;
    for (int i=1;i<=n;i++) a[i] = a[i] % C + 1;
    a[n+1]=a[1];
    inc(i,2,n+1)s+=(double)min(a[i],a[i-1])/a[i]/a[i-1];
    printf("%.3lf
",s);
    return 0;
}