import math
def trapez_rule(f,a,b,n):
    h = (b-a)/n
    s = f(a)+f(b)
    for i in xrange(1,n):
        s += 2.0*f(a+i*h)
    return s*h/2
print trapez_rule(lambda x: math.e**(-x**2), -1.0,1.0,100)