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

Zcnt, Ocnt = S.count("0"), S.count("1")
rate = 1200
Ans = 0
nowAC = 0

if Zcnt > Ocnt:
    ACcnt = 0
    while ACcnt != Ocnt and nowAC + Ocnt < A:
        ACcnt = 0
        for s in S:
            if s == "0":
                rate -= 1
            elif rate <= 1199:
                ACcnt += 1
                rate += 1
                nowAC += 1
        Ans += N
    
    if nowAC + Ocnt >= A:
        while nowAC < A:
            for s in S:
                if s == "0":
                    rate -= 1
                elif rate <= 1199:
                    rate += 1
                    nowAC += 1
                Ans += 1
                if nowAC == A:
                    break
    else:
        roop = (A - nowAC - 1) // Ocnt 
        nowAC += roop*Ocnt
        Ans += roop*N
        for s in S:
            Ans += 1
            if s == "1":
                nowAC += 1
            if nowAC == A:
                break
    
    print(Ans)

else:
    rateLog = [1200]
    ACLog = []
    ROOP = False
    while not ROOP and nowAC + Ocnt < A:
        ACcnt = 0
        for s in S:
            if s == "0":
                rate -= 1
            elif rate <= 1199:
                rate += 1
                nowAC += 1
                ACcnt += 1
        Ans += N
        ACLog.append(ACcnt)
        if rate in rateLog:
            ROOP = True
        else:
            rateLog.append(rate)
    
    if nowAC + Ocnt >= A:
        while nowAC < A:
            for s in S:
                if s == "0":
                    rate -= 1
                elif rate <= 1199:
                    rate += 1
                    nowAC += 1
                Ans += 1
                if nowAC == A:
                    break
    else:
        roop_start = rateLog.index(rate)
        roop_length = len(ACLog) - roop_start
        roop_AC = sum(ACLog[roop_start:])

        roop = (A - nowAC - 1) // roop_AC
        nowAC += roop*roop_AC
        Ans += roop*roop_length*N

        while nowAC < A:
            for s in S:
                if s == "0":
                    rate -= 1
                elif rate <= 1199:
                    rate += 1
                    nowAC += 1
                Ans += 1
                if nowAC == A:
                    break
    print(Ans)