#include <cstdio>

 #include <cstring>

 #include <algorithm>

 #include <iostream>

 #include <queue>

 using namespace std;

 const int maxn=+;

 int a[maxn];

 long long f[maxn];

 long long sum[maxn];

 int n;

 long long m;

 int main(){

     scanf("%d%lld",&n,&m);

     sum[]=;

     int ok=;

     for(int i=;i<=n;i++){

         scanf("%d",&a[i]);

         sum[i]=sum[i-]+a[i];

         if(a[i]>m)ok=;

     }

     if(!ok){printf("-1");return ;}

     f[]=;

     f[]=a[];

     deque<int>q;

     int beg=;

     for(int i=;i<=n;i++){

             while(!q.empty()&&a[i]>=a[q.back()])q.pop_back();

             while(sum[i]-sum[beg-]>m&&beg<i)beg++;

             q.push_back(i);

             while(q.front()<beg&&!q.empty())q.pop_front();

             f[i]=f[beg-]+a[q.front()];

             for(int k=;k<=q.size();k++){

                 int b=q.front();

                 q.pop_front();

                 if(!q.empty())

                 f[i]=min(f[i],f[b]+a[q.front()]);

                 q.push_back(b);

             }

     }

     printf("%lld",f[n]);

 return ;

 }