9 13
6 14 19 5 -5 6 -10 20 8
 8 9
6 -1 5 -5 -8 -7 -8 -7
 10 7
-9 3 -4 -22 4 -17 0 -14 3 -2
 6 2
-2 3 0 -2 0 0
 5 10
-8 -24 0 -22 12
 5 13756
-2 -9 -10 0 10
 7 3
1 -3 0 3 -1 0 2
 9 9
-3 2 0 -2 -7 -1 0 5 3
 2 3
2 0
 19 78701
1 0 -1 0 -1 -1 0 1 0 -1 1 1 -1 1 0 0 -1 0 0
 5 4
-1 0 0 1 -1
 6 4
-1 0 2 -4 0 5
 20 23036
-1 1 -1 -1 -1 -1 1 -1 -1 0 0 1 1 0 0 1 0 0 -1 -1
 5 4
-1 0 -3 0 3
 12 82016
1 -2 -1 -1 -2 -1 0 -2 -1 1 -2 2
 7 4
-6 0 2 -3 0 4 0
 4 4
2 2 0 1
 6 1
-3 0 0 0 -2 3
 8 26
-4 9 -14 -11 0 7 23 -15
 20 23079
0 1 1 -1 1 0 -1 -1 0 0 1 -1 1 1 1 0 0 1 0 1
 1 1
1
 7 8555
-2 -3 -2 3 0 -2 0
 4 100
-100 0 -50 100
 3 14
12 12 -8
 1 1
2
 10 23
9 7 14 16 -13 -22 24 -3 -12 14
 8 11
12 -12 -9 3 -22 -21 1 3
 19 49926
-2 0 2 0 0 -2 2 -1 -1 0 0 0 1 0 1 1 -2 2 2
 16 76798
-1 11 -7 -4 0 -11 -12 3 0 -7 6 -4 8 6 5 -10
 9 5
-2 0 3 -4 0 4 -3 -2 0

-1
 -1
 1
 1
 1
 1
 -1
 2
 0
 1
 1
 -1
 1
 1
 1
 1
 -1
 1
 -1
 0
 0
 1
 1
 -1
 -1
 -1
 -1
 1
 1
 1

import java.util.*;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;



public class D {
	public static void main(String args[]){
		FastScanner in = new FastScanner();
		PrintWriter out = new PrintWriter(System.out);
		int n = in.nextInt();
		int d = in.nextInt();
		
		int mon = 0;
		int bank = 0;
		int limit = -1;
		int added = -1;
		for(int c = 0; c < n; c++){	//Go through each money thing
			int i = in.nextInt();
			//System.out.println("i: "+i+ " mon before: "+mon+" limit: "+limit+" added: "+added);
			
			if(i != 0){
				mon += i;	//Add/take out the money we cur have
				if(mon > d){	//If we are over the limit
					int over = mon-d;
					if(over > added - limit){
						bank = -1;
						break;
					}
					else{
						limit += over;
						mon = d;
					}
				}
			}
			
			else{	//If we need to check our money
				if(mon >= 0) {
					//limit = added - mon;
					continue;	//No need to add more
				}
				else{
					int extra = (added - limit);
					mon -= extra;
					bank++;//Going to the bank
					limit = mon * -1;
					added = d-mon;
					mon = d;
				}
				
			}
			
		}
		System.out.println(bank);
	
	}
	
	
	
	
	

	static class FastScanner{
		BufferedReader br;
		StringTokenizer st;
		public FastScanner(String s) {
			try{
				br = new BufferedReader(new FileReader(s));
			}
			catch(FileNotFoundException e) {
				e.printStackTrace();
			}
		}
		public FastScanner(){
			br = new BufferedReader(new InputStreamReader(System.in));
		}
		
		String nextToken()	{
			while(st == null ||!st.hasMoreElements()){
				try {
				st = new StringTokenizer(br.readLine());}
				catch(IOException e) {
					e.printStackTrace();
				}			
			}
			return st.nextToken();
		}
		
		int nextInt() {
			return Integer.parseInt(nextToken());
		}
		long nextLong() {
			return Long.parseLong(nextToken());
		}
		double nextDouble() {
			return Double.parseDouble(nextToken());
		}
		String next() {
			return nextToken();
		}
		
	}

}
