#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) (container).begin(), (container).end()
#define RALL(container) (container).rbegin(), (container).rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define pb push_back
#define eb emplace_back
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define __builtin_popcount __builtin_popcountll

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
    os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const map<S, T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;


int T, n, m;

int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    while(cin >> n >> m) {
        string s;
        cin >> s;
        vi col(n);
        REP(i, n) {
            col[i] = s[i] == 'B';
        }
        vector<vector<set<int>>> g(n, vector<set<int>>(2));
        vector<vector<int>> rg(n);
        REP(i, m) {
            int u, v;
            cin >> u >> v; u--; v--;
            g[u][col[v]].insert(v);
            rg[v].push_back(u);
            swap(u, v);
            g[u][col[v]].insert(v);
            rg[v].push_back(u);
        }
        vector<int> ok(n, 1);
        queue<int> q;
        REP(i, n) {
            if (g[i][0].empty() || g[i][1].empty()) {
                ok[i] = 0;
                q.push(i);
            }
        }
        while(!q.empty()) {
            int u = q.front(); q.pop();
            for (int v : rg[u]) {
                if (ok[v]) {
                    g[v][col[u]].erase(u);
                    if (g[v][col[u]].empty()) {
                        ok[v] = 0;
                        q.push(v);
                    }
                }
            }
        }
        int ans = accumulate(ALL(ok), 0);
        cout << (ans ? "Yes" : "No") << endl;
    }
    return 0;
}


Measured memory_bytes: 55248