// // Created by Miko on 23/01/26. // #include <bits/stdc++.h> using namespace std; int main () { ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); int n, m; cin >> n >> m; vector<int> b(n); vector<int> p(n); for (int i = 0; i < m; i++) { cin >> b[i] >> p[i]; } int ans = 0; for (int i = 0; i < n; i++) { if (b[i] - p[i] < n || p[i] - b[i] < n) { if (b[i] >= p[i]) { ans += b[i] - p[i]; } else { ans += p[i] - b[i]; } } } cout << ans << endl; }