N, Q = map(int, input().split())
S = input()

alpha =['a','b','c','d','e','f','g','h','i','j','k','l','m','n',
        'o','p','q','r','s','t','u','v','w','x','y','z']

data = ['' for _ in range(int(N*(N+1)/2))]

for i in range(N):
    for j in range(i,N):
        for k in range(26):
            c = S.count(alpha[k], i, j+1)
            data[int(N*i+j-i*(i+1)/2)] += alpha[k]*c
            
L = []
Y = [[] for _ in range(Q)]

for i in range(Q):
    L.append(list(map(int, input().split())))

for i in list(set([p[0] for p in L])):
    a = [[j, x] for j, x in enumerate(L) if x[0] == i]
    for k in list(set([q[1][1] for q in a])):
        b = [[y[1][2], y] for y in a if y[1][1] == k]
        for l in list(set([r[0] for r in b])):
            for m in b:
                if l==m[0]:
                    Y[m[1][0]] = data[int(N*(i-1)+k-1-i*(i-1)/2)][l-1]
                    
for i in range(Q):
    print(Y[i])