#include <iostream>
#include <vector>
#include <set>
using namespace std;
int main(){
ios_base::sync_with_stdio(false); cin.tie(nullptr);
int N, k; cin >> N >> k;
vector<int>strips;
strips.insert (strips.begin(), N);
for(int i = 0; i<k; i++){
int pos, l; cin >> pos >> l;
int or_l = strips[pos-1];
strips.erase(strips.begin() + pos - 1);
strips.insert(strips.begin() + pos - 1, l);
strips.insert(strips.begin() + pos, or_l - l);
}
set<int>distinct;
for(int i=0; i<strips.size(); i++){
//cout << strips[i] << " ";
distinct.insert(strips[i]);
}
cout << distinct.size() << '\n';
return 0;
}
