【 Gym - 101138F 】GukiZ Height （数学）

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <cmath>
#define N 100005
#define ll long long
#define ld long double
using namespace std;
ll n,h,a,s[N],ans=1LL<<60;
int main() {
	scanf("%lld%lld",&n,&h);
	for(int i=0;i<n;i++){
		scanf("%lld",&a);
		s[i+1]=s[i]+a;
	}
	for(ll i=1;i<=n;i++){
		if(h-i*(i+1)/2<=s[i]){
			ans=i;
			break;
		}else{
			ld a=n*n,b=(ld)2*i*n+n+2*s[n],c=(ld)i*i+i-2*h+2*s[i];
			ans=min(ans,(ll)ceil((-b+sqrtl(b*b-a*c*4))/(a*2))*n+i);
		}
	}
	printf("%lld\n",ans);
	return 0;
}