#include<bits/stdc++.h>
using namespace std;
#define ioio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define endl "\n"
#define P pair
#define P1 first
#define P2 second
#define u_map unordered_map
#define p_queue priority_queue
typedef long long ll;
const double eps=1e-6;
const int INF=0x3f3f3f3f;
const int mod=1e9+7;
const int N=1e6+7;
int dx[]={0,0,1,-1},dy[]={1,-1,0,0};
/*-------------------------------------*/

ll n,m;
ll a[N],st[N][22],sum[N];
ll c[N];
ll dp[N];
int q[N<<3],t=1,w;
bool used[N];
struct node {
	ll id,x,y;
	friend bool operator < (node a,node b) {
		return a.x + a.y > b.x + b.y;
	}   
};
p_queue<node> h;

int query(int l,int r){
	int k=log2(r-l+1);
	return max(st[l][k],st[r-(1<<k)+1][k]);
}
int main(){
	ioio   
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		st[i][0]=a[i];
		sum[i]=sum[i-1]+a[i];
		if(a[i]>m){
			cout<<-1<<endl;
			return 0;
		}
	}
	c[0]=1;
	for(int i=1;i<=n;i++)
		for(int j=c[i-1];j<=n;j++)
			if(sum[i]-sum[j-1]<=m){
		c[i]=j;
		break;
	}
	for(int j=1;j<=21;j++)
		for(int i=1;i+(1<<j)-1<=n;i++)
			st[i][j]=max(st[i][j-1],st[i+(1<<(j-1))][j-1]);
	for (int i=1; i<=n; i++) {
		dp[i]=INF;
		dp[i] = min(dp[i],dp[c[i] - 1] + query(c[i],i));
		while (t <= w && sum[i] - sum[q[t]] > m) {
			used[q[t]] = 1;
			t++;
		}
		while (t <= w && a[q[w]] < a[i]) {
			used[q[w]] = 1;
			w--;
		}
		q[++w] = i;
		if (t < w) 
			h.push({q[w - 1],dp[q[w - 1]],a[i]});
		while (!h.empty() && (used[h.top().id] || h.top().y < query(h.top().id + 1,i)))
			h.pop();
		if (!h.empty())
			dp[i] = min(dp[i],h.top().x + h.top().y); 
	}
	cout<<dp[n]<<endl;
	return 0;
}