#include <stdio.h>
#include <stdlib.h>
#define N 200000
int min(int a, int b) { return a < b ? a : b; }
int *ej[N], eo[N];
void append(int i, int j) {
int o = eo[i]++;
if (o >= 2 && (o & o - 1) == 0)
ej[i] = (int *) realloc(ej[i], o * 2 * sizeof *ej[i]);
ej[i][o] = j;
}
void bfs(int *dd, int n, int s) {
static int qu[N];
int i, head, cnt;
for (i = 0; i < n; i++)
dd[i] = n;
head = cnt = 0;
dd[s] = 0, qu[head + cnt++] = s;
while (cnt) {
int d, o;
i = qu[cnt--, head++], d = dd[i] + 1;
for (o = eo[i]; o--; ) {
int j = ej[i][o];
if (dd[j] > d)
dd[j] = d, qu[head + cnt++] = j;
}
}
}
int dda[N], ddb[N], dd_[N]; char visited[N];
void dfs(int i) {
int o;
if (visited[i])
return;
dd_[i] = dda[i], visited[i] = 1;
for (o = eo[i]; o--; ) {
int j = ej[i][o];
if (dda[j] == dda[i] - 1 && ddb[j] == ddb[i] - 1) {
dfs(j);
dd_[i] = min(dd_[i], dd_[j]);
}
}
}
int main() {
int n, m, s, t, a, b, i, j, d;
scanf("%d%d%d%d%d%d", &n, &m, &s, &t, &a, &b), s--, t--, a--, b--;
for (i = 0; i < n; i++)
ej[i] = (int *) malloc(2 * sizeof *ej[i]);
while (m--) {
scanf("%d%d", &i, &j), i--, j--;
append(i, j), append(j, i);
}
bfs(dda, n, a);
bfs(ddb, n, b);
d = dda[s] > dda[t] || ddb[s] > ddb[t] ? -1 : min(dda[t] - dda[s], ddb[t] - ddb[s]);
if (d != -1 && dda[s] == ddb[s] && dda[t] == ddb[t]) {
dfs(s), dfs(t);
if (dd_[s] > dd_[t])
d--;
}
printf("%d\n", d);
return 0;
}
