#include using namespace std; #include using namespace atcoder; using mint=modint998244353; //1000000007; using ll=long long; using pp=pair; #define sr string #define vc vector #define fi first #define se second #define rep(i,n) for(int i=0;i<(int)n;i++) #define pb push_back #define all(v) v.begin(),v.end() #define pque priority_queue #define bpc(a) __builtin_popcount(a) int main(){ int n,m;cin>>n>>m; vcv(m); rep(i,m)cin>>v[i]; int ac=0,wa=m; double ans=v[0]-1; while(wa-ac>1){ int x=(wa+ac)/2; double s=0; for(int i=x+1;i(double)n-v[x])wa=x; else ac=x; } double s=0; for(int i=ac+1;i