import sys

def main():
    #n, m = map(int, sys.stdin.readline().split(" "))
    sys.stdin.readline()
    
    prevLine = None
    distance = 0
    for line in sys.stdin:
        curLine = []
        for i, c in enumerate(line):
            if c == '\n':
                break
            if c == '&':
                curLine.append(0)
            else:
                curLine.append(max(0 if i == 0 else curLine[i-1], 0 if prevLine is None else prevLine[i]) + 1)
                if curLine[-1] > distance:
                    distance = curLine[-1]
        prevLine = curLine
    print distance

if __name__ == "__main__":
    main()