from collections import defaultdict

n, m = map(int,input().split())
S = input()
ind = defaultdict(list)
for i,s in enumerate(S):
    ind[s].append(i)

edge = [[] for _ in range(n)]
for _ in range(m):
    u, v = map(lambda x:int(x)-1,input().split())
    edge[u].append(v)
    edge[v].append(u)
  
D = {}
C = {}
A = {}
for i in ind["P"]:
    for to in edge[i]:
        if S[to] == "D":
            D[str(i)+str(to)] = 1
#print(D)
            
for i in D.keys():
    j = int(i[-1])
    for to in edge[j]:
        if S[to] == "C":
            C[i+str(to)] = 1
#print(C)

for i in C.keys():
    j = int(i[-1])
    for to in edge[j]:
        if S[to] == "A":
            A[i+str(to)] = 1
            
#print(A)

print(len(A.keys()))