parseInt(x) = parse(Int, x)
parseBigInt(x) = parse(BigInt, x)
parseFloat(x) = parse(Float64, x)
parseBigFloat(x) = parse(BigFloat, x)
parseMap(x::Array{SubString{String},1}) = map(parseInt, x)

function main()
    n=parseInt(readline())
    s=chomp(readline())
    b=count(x->x=='#',s)
    println(min(b,n-b))
end
main()