n,m,k=list(map(int,input().split()))
black_longth=[]
array=[i for i in input()]
number=[1 if i=='o' else 0 for i in array]
for _ in range(n-1):#竖向找出连续的最长'o'字符串
    middle=[i for i in input()]
    for i in range(m):
        if middle[i]==array[i]=='o':
            number[i]+=1
        elif middle[i]=='o':
            number[i]=1
        else:
            if number[i]:
                black_longth.append(number[i])
                number[i]=0
    array=middle
for i in range(m):
    if number[i]:
        black_longth.append(number[i])
black_longth.sort(reverse=True)#从大到小排序
result=0
for i in black_longth:#依次遍历,直至i为1
    if i==1:
        break
    if i >=k:
        result+=(k-1)
        break
    else:
        result+=(i-1)
        k-=i
print(result)