#include <bits/stdc++.h>

using namespace std;
const int N = 10010;
int b[N];
int l;
int m;
int cnt;

int main() {
    scanf("%d %d", &l, &m);
    for (int i = 0; i <= l; i++) b[i] = 1;

    while (m--) {
        int u, v;
        scanf("%d %d", &u, &v);
        for (int i = u; i <= v; i++) b[i]--;
    }
    for (int i = 0; i <= l; i++)
        if (b[i] == 1) cnt++;

    printf("%d", cnt);
    return 0;
}