#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, k;
if (!(cin >> n >> k)) return 0;
vector<int> strips;
strips.reserve(k + 1);
strips.push_back(n);
for (int i = 0; i < k; ++i) {
int x, l;
cin >> x >> l;
int idx = x - 1;
int len = strips[idx];
int left = l;
int right = len - l;
strips[idx] = left;
strips.insert(strips.begin() + idx + 1, right);
}
vector<bool> seen(1'000'001, false);
for (int v : strips) {
seen[v] = true;
}
int ans = 0;
for (bool b : seen) ans += b;
cout << ans << '\n';
return 0;
}
