How it is giving run-time error?

general
,
1

#include<bits/stdc++.h>
using namespace std;

void solve()
{long long n,m;
cin>>n>>m;

  long long arr[n]={0};
   
   while(m--)
     {
          long long x,y;
          cin>>x>>y;

          for(long long i=0;i<n;i++)
            {
               if((i+1)%y!=0 && arr[i]<x)
                  {
                       arr[i]=x;
                  }
            } 
     }
    long long sum=0;
    for(long long i=0;i<n;i++)
     {
       sum=sum+arr[i];
     }
    cout<<sum<<endl;


}

int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);

long long t;
cin >> t;

while(t--){
   solve();
    }
return 0;

}