Failed to save to directory from Python

I have the following code. The goal is to save some graphics in pdf format in a directory that I created using os.mkdir ("...") but I get the following error:

IOError: [Errno 13] Permission denied: '\ enva1.pdf'

I do not know if the bug is python or because of security problems in my directory.

from __future__ import division 

import numpy as np
import matplotlib.pyplot as plt

import os

import re

os.chdir("./envolventes")

diractual = os.getcwd()

ficheros = os.listdir(diractual)

lista_limpia = [ x for x in ficheros if ("D" not in x) & (int(re.match('.*?([0-9]+).TXT', x).group(1)) <= 45)]

os.mkdir("./GRAFICAS")

for p in range(1,46):
fig=plt.figure('Aceleraciones')
plt.title('Punto ' + str(p))


for t in range(1,11):       # Los 10 trenes
    filename='T' + str(t) + 'A' + str(p) + '.TXT'
    archivo=open(filename)

    lineas=archivo.readlines()
    lineas.append('0')
    datos=lineas[13:415]

    velocidades=[]
    aceleraciones=[]

    for i in datos[:]:
        v=i[9:17]
        velocidades.append(float(v))
        a=i[31:45]
        aceleraciones.append(float(a))

    line,=plt.plot(velocidades,aceleraciones,label=r"A"+str(t))

plt.xlabel(r'km/h')                #Etiqueta del eje x
plt.ylabel(r'm/s2')                #Etiqueta del eje y

plt.legend(loc=0)
plt.show()

fig.savefig("\enva"+str(p)+".pdf")