#include <cstdio>

int main()
{
    freopen(".10.in","r",stdin);
    freopen(".10.out","w",stdout);

    int n, S[110], C[110], sum = 0;
    scanf("%d", &n);
    for(int i = 0 ; i < n ; i++ )
        scanf("%d", S+i);
    for(int i = 0 ; i < n ; i++ )
        scanf("%d", C+i);
    for(int i = 0 ; i < n ; i++ )
        if( S[i] >= 30 ) sum+=S[i];
        else if( C[i] == 1 ) sum += 30;
        else sum += S[i];
    printf("%.2lf", (double)sum/n);
}