#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int MAXN = 30010;
const ll ZERO = 0;
const ll INF = LLONG_MAX;
vector<ll> p2bs[MAXN];
vector<pair<ll,ll>> p2d[MAXN];
vector<int> col2p[MAXN];
vector<int> powers;
int p2id[MAXN];
int get_id(int x){
return p2id[x+1];
}
const int BLOCK = 900;
ll ans1[BLOCK][MAXN];
vector<pair<ll,ll>> ans2[MAXN];
// void print(){
// for(int i = 0; i < MAXN; ++i){
// if(ans[i].empty()) continue;
// cout << i << ":\n";
// for(auto [x, val] : ans[i]){
// cout << "\t" << x << ": " << val << "\n";
// }
// }
// cout << "================\n";
// }
ll& ans_at(int p, ll x){
int id = get_id(p);
if(id < BLOCK) return ans1[id][x];
else
return lower_bound(ans2[id].begin(), ans2[id].end(), make_pair(x, ZERO))->second;
}
int32_t main(){
cin.tie(NULL)->sync_with_stdio(false);
int n, m; cin >> n >> m;
int B[2], P[2];
cin >> B[0] >> P[0];
cin >> B[1] >> P[1];
powers.push_back(-1);
for(int i = 2; i < m; ++i){
int b, p; cin >> b >> p;
p2bs[p].push_back(b);
powers.push_back(p);
}
sort(powers.begin(), powers.end());
powers.erase(unique(powers.begin(), powers.end()), powers.end());
for(int i = 0; i < powers.size(); ++i){
p2id[powers[i]+1] = i;
}
for(int p = 1; p < MAXN; ++p){
map<int, int> D;
sort(p2bs[p].begin(), p2bs[p].end());
p2bs[p].erase(unique(p2bs[p].begin(), p2bs[p].end()), p2bs[p].end());
queue<int> q;
for(auto b : p2bs[p]){
col2p[b].push_back(p);
q.push(b);
D[b] = 0;
}
while(q.size()){
auto x = q.front(); q.pop();
if(x - p >= 0 && D.count(x - p) == 0){
D[x - p] = D[x] + 1;
q.push(x - p);
}
if(x + p < n && D.count(x + p) == 0){
D[x + p] = D[x] + 1;
q.push(x + p);
}
}
vector<pair<ll,ll>> v;
for(auto [a, b] : D){
v.push_back({a, b});
if(get_id(p) >= BLOCK) ans2[get_id(p)].push_back({a, INF});
}
p2d[p] = move(v);
}
for(int i = 0; i < BLOCK; ++i){
for(int j = 0; j < n; ++j){
ans1[i][j] = INF;
}
}
struct Node{
int i, x;
// se i == -1, eh col
ll cost;
bool operator<(const Node &n) const{
return cost > n.cost;
}
};
priority_queue<Node> pq;
deque<Node> q;
for(int i = (B[0] % P[0]); i < n; i += P[0]){
int dist = abs(i - B[0]) / P[0];
pq.push({-1, i, ans_at(-1, i) = dist});
}
// print();
while(pq.size() + q.size() > 0){
auto qry_p2d = [&](int p, ll x){
return lower_bound(p2d[p].begin(), p2d[p].end(), make_pair(x, ZERO))->second;
};
auto maybe_update = [&](int p, int x, ll val, ll d){
if(ans_at(p, x) > val){
Node X = {p, x, ans_at(p, x) = val};
if(d == 0) q.push_front(X);
else if(d == 1) q.push_back(X);
else pq.push(X);
}
};
Node nxt;
{
if(q.empty()){
nxt = pq.top();
pq.pop();
}else if(pq.empty()){
nxt = q.front();
q.pop_front();
}else{
if(q.front().cost <= pq.top().cost){
nxt = q.front();
q.pop_front();
}else{
nxt = pq.top();
pq.pop();
}
}
}
auto [i, x, cost] = nxt;
if(cost > ans_at(i, x)) continue;
// cout << i << " " << x << " " << cost << "\n";
if(i == -1){
for(auto p : col2p[x]){
maybe_update(p, x, cost + qry_p2d(p, x), 2);
}
}else{
// sou power i na coluna x
maybe_update(-1, x, cost, 0);
if(x + i < n){
maybe_update(i, x + i, cost + 1, 1);
}
if(x - i >= 0){
maybe_update(i, x - i, cost + 1, 1);
}
}
// print();
}
// print();
cout << ((ans1[0][B[1]] == LLONG_MAX)? -1 : ans1[0][B[1]]) << "\n";
}
