#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{

int s,n;
cin >> s >> n;
vector<pair<int,int> >c;
int w,h;
    for(int i=0;i<n;i++)
    {
        cin >> w;
        cin >> h;
        c.push_back({min(w,h),max(w,h)})
    }

sort(c.begin(), c.end());
int aux,p=0;
    for(int i=0;i<c.size();i++)
    {
        aux=c[i].first+c[i].second+1;
        if(aux<=s)
        {
            p++;
            s--;
        }
    }
    cout<<p;
    return 0;
}