#include <iostream>
using namespace std;

int main(){
  int t,n;
  while(1){
    cin >> t;
    if(t==0) break;
    cin >> n;
    for(int i=0;i<n;i++){
      int s,f;
      cin >> s>> f;
      t-=f-s;
    }
    if(t<=0) cout << "OK"<<endl;
    else cout<<t<<endl;
  }
  
  return 0;
}