【BZOJ 2301】 单选错位

..

 #include <cstdio>

#include <cmath>
#include <algorithm>
using namespace std;
#define LL long long
LL n,A,B,C,a[10000000+1];
int main()
{
    
    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;
    
    double ans=0;
    for(int i=1;i<n;i++) ans+=1.0/max(a[i],a[i+1]);
    ans+=1.0/max(a[1],a[n]);
    printf("%.3lf\n",ans);
    
    
    return 0;
}