#include <bits/stdc++.h>
#define ll int
#define ld long double
#define pb push_back
#define endl "\n"
#define fr first
#define sc second
#define sz size()
#define bc back()
using namespace std;
const ll N=2e3+7;
ll n,d[N];
vector <vector <pair<ll,ll>> > g(N);
void dijkstra(ll val){
set <pair<ll,ll>> q;
q.insert({0,val});
d[val]=0;
while(!q.empty()){
ll x=q.begin()->sc;
q.erase(q.begin());
for(auto i : g[x]){
ll len=i.sc,to=i.fr;
if(d[to]>d[x]+len){
q.erase({d[to], to});
d[to]=d[x]+len;
q.insert({d[to],to});
}
}
}
}
void solve(){
ll i,j,q,b,c,m,t;
ll k;
cin>>n>>m;
for(i=0;i<m;i++){
cin>>b>>t;
if(i==0) k=b;
if(i==1) q=b;
c=0;
for(j=b+t;j<n;j+=t){
c++;
g[b].pb({j,c});
}
c=0;
for(j=b-t;j>=0;j-=t){
c++;
g[b].pb({j,c});
}
}
for(i=0;i<n;i++) d[i]=inf;
dijkstra(k);
if(d[q]==inf) cout<<-1<<endl;
else cout<<d[q]<<endl;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
ll t=1;
while(t--) solve();
}
/*
5 3
0 2
1 1
4 1
*/
Compilation message
skyscraper.cpp: In function 'void solve()':
skyscraper.cpp:50:27: error: 'inf' was not declared in this scope; did you mean 'ynf'?
50 | for(i=0;i<n;i++) d[i]=inf;
| ^~~
| ynf
skyscraper.cpp:52:14: error: 'inf' was not declared in this scope; did you mean 'ynf'?
52 | if(d[q]==inf) cout<<-1<<endl;
| ^~~
| ynf
