#include<bits/stdc++.h>
using namespace std;
#define int long long
const int MAXN = 30010;
vector<int> p2bs[MAXN];
unordered_map<int,int> p2d[MAXN];
vector<int> col2p[MAXN];
unordered_map<int,int> ans[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";
}
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];
for(int i = 2; i < m; ++i){
int b, p; cin >> b >> p;
p2bs[p].push_back(b);
}
for(int p = 1; p < MAXN; ++p){
auto &D = p2d[p];
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);
}
}
}
// cout << "P2D\n";
// for(int p = 1; p < MAXN; ++p){
// if(p2d[p].empty()) continue;
// cout << p << ": \n";
// for(auto [x, val] : p2d[p]){
// cout << "\t" << x << " " << val << endl;
// }
// }
// cout << "================\n";
struct Node{
int i, x;
// se i == -1, eh col
int cost;
bool operator<(const Node &n) const{
return cost > n.cost;
}
};
priority_queue<Node> pq;
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[0][i] = dist});
}
// print();
while(pq.size()){
auto maybe_update = [&](int p, int x, int val){
if(ans[p + 1].count(x) == 0 || ans[p + 1][x] > val){
pq.push({p, x, ans[p + 1][x] = val});
}
};
auto [i, x, cost] = pq.top(); pq.pop();
if(cost > ans[i + 1][x]) continue;
// cout << i << " " << x << " " << cost << "\n";
if(i == -1){
for(auto p : col2p[x]){
maybe_update(p, x, cost + p2d[p][x]);
}
}else{
// sou power i na coluna x
maybe_update(-1, x, cost);
if(x + i < n){
maybe_update(i, x + i, cost + 1);
}
if(x - i >= 0){
maybe_update(i, x - i, cost + 1);
}
}
// print();
}
// print();
if(ans[0].count(B[1]) == 0) cout << -1 << "\n";
else cout << ans[0][B[1]] << "\n";
}
