#include<bits/stdc++.h>
using namespace std;
const int maxn = 10000;
int sum[(maxn << 2) + 60], add[(maxn << 2) + 60];

void push_up(int rt) {
    sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
    return;
}

void push_down(int rt, int m) {
    if (add[rt]) {
        add[rt << 1] = add[rt];
        add[rt << 1 | 1] = add[rt];
        sum[rt << 1] = (m - (m >> 1)) * add[rt];
        sum[rt << 1 | 1] = (m >> 1) * add[rt];
        add[rt] = 0;
    }
    return;
}

void update(int a, int b, int c, int l, int r, int rt) {
    if (a <= l && b >= r) {
        sum[rt] = (r - l + 1) * c;
        add[rt] = c;
        return;
    }
    push_down(rt, r - l + 1);
    int mid = (l + r) >> 1;
    if (a <= mid) {
        update(a, b, c, l, mid, rt << 1);
    }
    if (b > mid) {
        update(a, b, c, mid + 1, r, rt << 1 | 1);
    }
    push_up(rt);
    return;
}

int query(int a, int b, int l, int r, int rt) {
    if (a <= l && b >= r) {
        return sum[rt];
    }
    push_down(rt, r - l + 1);
    int mid = (l + r) >> 1, ans = 0;
    if (a <= mid) {
        ans += query(a, b, l, mid, rt << 1);
    }
    if (b > mid) {
        ans += query(a, b, mid + 1, r, rt << 1 | 1);
    }
    return ans;
}

int main(void) {
	int n, m;
	scanf("%d %d", &n, &m);
	while (m--) {
        int l, r;
        scanf("%d %d", &l, &r);
        update(l, r, 1, 0, n, 1);
	}
	printf("%d", n + 1 - query(0, n, 0, n, 1));
	return 0;
}