NX = (int, input())  
SX = list(input())
A = 0
B = 0
C = 0
D = 0
E = 0
F = 0
G = 0
H = 0
I = 0
J = 0
K = 0
L = 0
M = 0
N = 0
O = 0
P = 0
Q = 0
R = 0
S = 0
T = 0
U = 0
V = 0
W = 0
X = 0
Y = 0
Z = 0
SX.sort()
for i in SX:
    if i == "A":
        A += 1
    elif i == "B":
        B += 1
    elif i == "C":
        C += 1
    elif i == "D":
        D += 1
    elif i == "E":
        E += 1
    elif i == "F":
        F += 1
    elif i == "G":
        G += 1
    elif i == "H":
        H += 1
    elif i == "I":
        I += 1
    elif i == "J":
        J += 1
    elif i == "K":
        K += 1
    elif i == "L":
        L += 1
    elif i == "M":
        M += 1
    elif i == "N":
        N += 1
    elif i == "O":
        O += 1
    elif i == "P":
        P += 1
    elif i == "Q":
        Q += 1
    elif i == "R":
        R += 1
    elif i == "S":
        S += 1
    elif i == "T":
        T += 1
    elif i == "U":
        U += 1
    elif i == "V":
        V += 1
    elif i == "W":
        W += 1
    elif i == "X":
        X += 1
    elif i == "Y":
        Y += 1
    else:
        Z += 1
XX = [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]
XX.sort(reverse=True)
XX_str = map(str, XX)
print("".join(XX_str))