bzoj2134

题解：

每一题对的概率为min(a[i],a[i+1])/a[i]/a[i+1];

即可

代码：

#include<bits/stdc++.h>
using namespace std;
const int N=;
int a[N],n,A,B,C;
int main()
{
    scanf("%d%d%d%d%d",&n,&A,&B,&C,&a[]);
    for (int i=;i<=n;i++)a[i]=((long long)a[i-]*A+B)%;
    for (int i=;i<=n;i++)a[i]=a[i]%C+;
    double ans=;
    for (int i=;i<n;i++)
     ans+=(double)min(a[i],a[i+])/a[i]/a[i+];
    printf("%.3lf",ans+(double)min(a[],a[n])/a[]/a[n]);
}