题面
Sol
第\(i\)道题选对的概率就是\(\frac{min(a[i-1], a[i])}{a[i]*a[i-1]}\)
# include <bits/stdc++.h>
# define RG register
# define IL inline
# define Fill(a, b) memset(a, b, sizeof(a))
using namespace std;
typedef long long ll;
const int _(1e7 + 5);
const int Zsy(1e8 + 1);
IL int Input(){
RG int x = 0, z = 1; RG char c = getchar();
for(; c < '0' || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;
for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
return x * z;
}
int n, a[_];
double ans;
int main(RG int argc, RG char* argv[]){
n = Input(); RG int A = Input(), B = Input(), C = Input(); a[1] = Input();
for(RG int i = 2; i <= n; ++i) a[i] = (1LL * a[i - 1] * A % Zsy + B) % Zsy;
for(RG int i = 1; i <= n; ++i) a[i] = a[i] % C + 1;
a[0] = a[n];
for(RG int i = 1; i <= n; ++i) ans += 1.0 * min(a[i - 1], a[i]) / (1.0 * a[i] * a[i - 1]);
printf("%.3lf\n", ans);
return 0;
}