using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
static class Program{
	const int mod=(int)1e9+7;
	static List<int>[] li;
	static int[][] b;
	static bool[][] bb;
	static int[] h;
	static string t,ans="No";
	static void Main(){
		Sc sc=new Sc();
		var s=sc.Ia;
		int n=s[0],m=s[1];
		t="X"+sc.S;
		li=new List<int>[n+1];
		b=new int[2][];
		bb=new bool[2][];
		h=new int[n+1];
		var lij=new List<int>();
		for(int i=1;i<=n;i++){li[i]=new List<int>();}
		for(int i=0;i<m;i++){
			var e=sc.Ia;
			li[e[0]].Add(e[1]);
			if(e[0]!=e[1]){li[e[1]].Add(e[0]);}
			else{
				lij.Add(e[0]);
				h[e[0]]|=2;
			}
			if(t[e[0]]==t[e[1]]){
				h[e[0]]|=h[e[1]]|=1;
			}
		}
		b[0]=new int[n+1];
		b[1]=new int[n+1];
		bb[0]=new bool[n+1];
		bb[1]=new bool[n+1];
		for(int i = 1,j=1;i<=n&&ans=="No";i++) {
			if(b[0][i]==0){Fu(i,0,0,j);j++;}
			if(b[1][i]==0){Fu(i,1,0,j);j++;}
		}
		Console.WriteLine("{0}",ans);
	}
	static void Fu(int a,int g,int p,int j){
		b[g][a]=j;
		bb[g][a]=true;
		if(g==1){
			for(int i=0;i<li[a].Count;i++){
				if(t[a]!=t[li[a][i]]){
					if(b[0][li[a][i]]==0){
						Fu(li[a][i],0,a,j);
					}
					else if(bb[0][li[a][i]]){
						ans="Yes";break;
					}
				}
			}
		}
		else{
			for(int i=0;i<li[a].Count;i++){
				if(t[a]==t[li[a][i]]){
					if(b[1][li[a][i]]==0){
						Fu(li[a][i],1,a,j);
					}
					else if(bb[1][li[a][i]]){
						ans="Yes";break;
					}
				}
			}
		}
		bb[g][a]=false;
	}
}
public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),int.Parse);}
	public int[] Ia3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),long.Parse);}
	public long[] La3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),long.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}

Measured memory_bytes: 49580