#!/usr/bin/env python3
import sys
sys.setrecursionlimit(10 ** 9)

def main():
    N, M = map(int, input().split())
    S = input()
    pdca = "PDCA"
    ans = 0
    A = [pdca.index(ss) for ss in S]
    class DFS():
        def __init__(self, N: int) -> None:
            self.nodes = N                          # 頂点数
            self.G = [[] for _ in range(N)]         # グラフ
            self.seen = [False] * N                 # 各ノードが訪問済みかどうかのフラグ
            self.firstOrder = []                    # ノードの行きがけ順(0-index)
            self.lastOrder = []                     # ノードの帰りがけ順(0-index)

        # 辺の追加
        def addEdge(self, fromNode: int, toNode: int, bothDirection: bool):
            self.G[fromNode].append(toNode)
            if bothDirection:
                self.G[toNode].append(fromNode)
        # DFS
        def build(self, now: int, pre:int):
            nonlocal ans
            # ----- ノードに到着した時の処理
            # self.firstOrder.append(now)
            # self.seen[now] = True
            # ----- 隣接する各ノードへの移動処理
            for next in self.G[now]:
                # if self.seen[next]:
                if A[next] != pre + 1:
                    continue
                if pre + 1 == 3:
                    ans += 1
                self.build(next, pre + 1)
            # ----- ノードから戻る時の処理
            # self.lastOrder.append(now)
            return

    d = DFS(N)
    for _ in range(M):
        u, v = map(lambda i : int(i) - 1, input().split())
        d.addEdge(v, u, bothDirection=True)
    
    for i in range(N):
        if A[i] == 0:
            d.build(i, 0)
    print(ans)
    return

if __name__ == '__main__':
    main()