#include<bits/stdc++.h> using namespace std; int main() { int l, n, i, j, count = 0; scanf("%d%d", &l, &n); bool *tree = new bool[l + 1]; for (i = 0; i < l+1; i++) { tree[i] = true; } for (i = 0; i < n; i++) { int begin, end; scanf("%d%d", &begin, &end); j = begin; while (j <= end) { tree[j] = false; j++; } } for (i = 0; i < l + 1; i++) { if (tree[i] == true)count++; } printf("%d", count); delete []tree; return 0; }