//@formatter:off #include #define overload4(_1,_2,_3,_4,name,...) name #define rep1(i,n) for (ll i = 0; i < ll(n); ++i) #define rep2(i,s,n) for (ll i = ll(s); i < ll(n); ++i) #define rep3(i,s,n,d) for(ll i = ll(s); i < ll(n); i+=d) #define rep(...) overload4(__VA_ARGS__,rep3,rep2,rep1)(__VA_ARGS__) #define rrep1(i,n) for (ll i = ll(n)-1; i >= 0; i--) #define rrep2(i,n,t) for (ll i = ll(n)-1; i >= (ll)t; i--) #define rrep3(i,n,t,d) for (ll i = ll(n)-1; i >= (ll)t; i-=d) #define rrep(...) overload4(__VA_ARGS__,rrep3,rrep2,rrep1)(__VA_ARGS__) #define all(a) a.begin(),a.end() #define rall(a) a.rbegin(),a.rend() #define popcount(x) __builtin_popcountll(x) #define pb push_back #define eb emplace_back #ifdef __LOCAL #define debug(...) { cout << #__VA_ARGS__; cout << ": "; print(__VA_ARGS__); cout << flush; } #else #define debug(...) void(0) #endif #define INT(...) int __VA_ARGS__;scan(__VA_ARGS__) #define LL(...) ll __VA_ARGS__;scan(__VA_ARGS__) #define STR(...) string __VA_ARGS__;scan(__VA_ARGS__) #define CHR(...) char __VA_ARGS__;scan(__VA_ARGS__) #define DBL(...) double __VA_ARGS__;scan(__VA_ARGS__) #define LD(...) ld __VA_ARGS__;scan(__VA_ARGS__) using namespace std; using ll = long long; using ld = long double; using P = pair; using LP = pair; using vi = vector; using vvi = vector>; using vl = vector; using vvl = vector>; using vd = vector; using vvd = vector>; using vs = vector; using vc = vector; using vvc = vector>; using vb = vector; using vvb = vector>; using vp = vector

; using vvp = vector>; template istream& operator>>(istream &is,pair &p) { return is >> p.first >> p.second; } template ostream& operator<<(ostream &os,const pair &p) { return os<<'{'< istream& operator>>(istream &is,vector &v) { for(T &t:v){is>>t;} return is; } template ostream& operator<<(ostream &os,const vector &v) { os<<'[';rep(i,v.size())os< void vecout(const vector &v,char div='\n') { rep(i,v.size()) cout< bool chmin(T& a,T b) {if(a > b){a = b; return true;} return false;} template bool chmax(T& a,T b) {if(a < b){a = b; return true;} return false;} void scan(){} template void scan(Head& head, Tail&... tail){ cin >> head; scan(tail...); } template void print(const T& t){ cout << t << '\n'; } template void print(const Head& head, const Tail&... tail){ cout< void fin(const T&... a) { print(a...); exit(0); } struct Init_io { Init_io() { ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); cout << boolalpha << fixed << setprecision(15); } } init_io; const string yes[] = {"no","yes"}; const string Yes[] = {"No","Yes"}; const string YES[] = {"NO","YES"}; const int inf = 1001001001; const ll linf = 1001001001001001001; //@formatter:on int main() { INT(n, m); vi b(m); cin >> b; rep(i, m) b[i] = n - b[i]; reverse(all(b)); debug(b); double ok = b[0], ng = b.back(); auto f = [&](double x) -> bool { double d = 0; rep(i, m) d += min((double) b[i], x + 1); return d / m >= x; }; rep(_, 100) { double mid = (ok + ng) / 2; (f(mid) ? ok : ng) = mid; } fin(min((double) b.back(), ok + 1) + n - 1 - b.back()); }