Lennot

ip = [int(i) for i in raw_input().split()]
lennot = []
for i in range(ip[1]):
	lennot.append([int(j) for j in raw_input().split()])

cpt = {1: (0, 1)}
don = []
while not ip[0] in cpt:
	l = [lennot[i] for i in range(len(lennot)) if lennot[i][0] in cpt and lennot[i] not in don]
	m = min([cpt[i[0]][1]*(i[2]) + cpt[i[0]][0] for i in l])
	for i in l:
		a = cpt[i[0]][1]*(i[2]) + cpt[i[0]][0]
		if a == m:
			don.append(i)
			try:
				if a  < cpt[i[1]][0] + (cpt[i[1]][1]-cpt[i[0]][1]^1) * max([j[2] for j in lennot if j[0] == i[1]]):
					cpt[i[1]] = (a, cpt[i[0]][1]^1)
			except KeyError:
				cpt[i[1]] = (a, cpt[i[0]][1]^1)

			break
print cpt[ip[0]][0]
quit()

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: WRONG ANSWER

Test 7

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 8

Group: 2

Verdict: WRONG ANSWER

Test 9

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 10

Group: 2

Verdict: WRONG ANSWER

Test 11

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 12

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 13

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 14

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 15

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 16

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 17

Group: 3

Verdict: TIME LIMIT EXCEEDED