#include <bits/stdc++.h>
using namespace std;
const int N = 2e5+5;
int n, m, s, d, a, b;
int da[N], db[N], dp[N];
vector<int> g[N];
void bfs(int src, int d[]) {
fill_n(d, N, 1e9);
queue<int> Q;
Q.emplace(src), d[src] = 0;
while(!Q.empty()) {
int u = Q.front(); Q.pop();
for(int v : g[u]) if(d[u] + 1 < d[v])
Q.emplace(v), d[v] = d[u] + 1;
}
}
int dep[N];
int solve(int src) {
memset(dep, -1, sizeof dep);
queue<int> Q;
Q.emplace(src), dep[src] = 0;
int ret = 0;
while(!Q.empty()) {
int u = Q.front(); Q.pop();
ret = max(ret, dep[u]);
for(int v : g[u]) if(da[v] == da[u] - 1 && da[v] == db[v] && dep[v] == -1)
dep[v] = dep[u] + 1, Q.emplace(v);
}
return ret;
}
int main() {
memset(dp, -1, sizeof dp);
scanf("%d %d", &n, &m);
scanf("%d %d %d %d", &s, &d, &a, &b);
for(int i = 1, u, v; i <= m; i++) {
scanf("%d %d", &u, &v);
g[u].emplace_back(v), g[v].emplace_back(u);
}
bfs(a, da), bfs(b, db);
int w1 = da[d] - da[s], w2 = db[d] - db[s];
if(w1 != w2) printf("%d\n", max(-1, min(w1, w2)));
else printf("%d\n", max(-1, w1 - (w1 + solve(s) < solve(d))));
return 0;
}
