#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define Valerian_or_Habil ios::sync_with_stdio(false);cin.tie(0);
#define Valerian void
using namespace std;
Valerian solve(){
ll n, k;
cin >> n >> k;
vector<ll> v;
v.pb(n);
for (int i = 0; i < k; i++) {
ll g, h;
cin >> g >> h;
ll cur = v[g-1];
v.erase(v.begin() + (g-1));
v.insert(v.begin() + (g-1), cur - h);
v.insert(v.begin() + (g-1), h);
}
set<ll> s(v.begin(), v.end());
cout << s.size() << "\n";
}
int main(){
Valerian_or_Habil
ll t = 1;
while(t--){
solve();
}
return 0;
}
