n = int(input())
s = input()
index = 0
indexes = {}
best_result = None
for index in range(n):
    indexes[s[index]] = index
    if len(indexes) == 4:
        result = max(indexes.values()) - min(indexes.values()) + 1
        if best_result is None or result < best_result:
            best_result = result
print(best_result or -1)