def get_segment(l, r, s, c):
    v = []

    for i in range(len(s)):
        if (s[i] != c):
            continue
        v.append([l[i], r[i]])
    v.sort()
    seg = []

    it = 0

    while (it < len(v)):
        nit = it + 1
        rig = v[it][1]
        lef = v[it][0]

        while (nit < len(v) and v[nit][0] <= rig + 1):
            rig = max(rig, v[nit][1])
            nit += 1
        seg.append([lef, rig])
        it = nit
    return seg

def rev(seg):
    if (len(seg) == 0):
        return seg
    ans = []
    ans.append([1, 1000000000])
    prev = 1
    for i in range(len(seg)):
        if (seg[i][0] != prev):
            ans.append([prev, seg[i][0]])
        prev = seg[i][1] + 1
    if (prev != 1000000000):
        ans.append([prev + 1, 1000000000])
    return ans

def textFormatting(starting, ending, style):
    n = len(starting)
    l = starting
    r = ending
    s = style
    assert(1 <= n and n <= 100000)
    assert(len(l) == n and len(r) == n and len(s) == n)
    for i in range(n):
        assert(1 <= l[i] and l[i] <= r[i] and r[i] <= 1000000000)
        assert(s[i] == 'b' or s[i] == 'u' or s[i] == 'i')

    seg = []
    seg.append(get_segment(l, r, s, 'b'))
    seg.append(get_segment(l, r, s, 'u'))
    seg.append(get_segment(l, r, s, 'i'))

    res = 1000000000

    for a in range(2):
        for b in range(2):
            for c in range(2):
                if (a == 1 or b == 1 or c == 1):
                    continue
                x = seg[0]
                if (a == 1):
                    x = rev(seg[0])
                y = seg[1]
                if (b == 1):
                    y = rev(seg[1])
                z = seg[2]
                if (c == 1):
                    z = rev(seg[2])
                cur = len(x) + len(y) + len(z)
                q = []
                for i in x:
                    q.append(i)
                for i in y:
                    q.append(i)
                for i in z:
                    q.append(i)
                q.sort()
                it = 0

                while (it != len(q)):
                    nit = it
                    while (nit < len(q) and q[nit] == q[it]):
                        nit += 1
                    it = nit
                    cur += 1

                res = min(res, cur)
    return res