[HAOI2014]贴海报

#include <bits/stdc++.h>

using namespace std;
const int N = 1e7 + 10;

#define gc getchar()
#define lson jd << 1
#define rson jd << 1| 1 

int W[N << 2];
bool O[1010];
int js;

inline int read(){
    int x = 0, f = 1; char c = gc;
    while(c < ‘0‘ || c > ‘9‘) {if(c == ‘-‘) f = -1; c = gc;}
    while(c >= ‘0‘ && c <= ‘9‘) x = x * 10 + c - ‘0‘, c = gc;
    return x * f;
}

void Sec_G(int l, int r, int jd, int x, int y, int g){
    if(x <= l && r <= y) {W[jd] = g; return ;}
    if(W[jd]) {W[lson] = W[jd], W[rson] = W[jd], W[jd] = 0;    }
    int mid = (l + r) >> 1;
    if(x <= mid) Sec_G(l, mid, lson, x, y, g);
    if(y > mid) Sec_G(mid + 1, r, rson, x, y, g);
}

void dfs_tree(int l, int r, int jd){
    if(l == r) {O[W[jd]] = 1; return ;}
    if(W[jd]) {W[lson] = W[jd]; W[rson] = W[jd];}
    int mid = (l + r) >> 1;
    dfs_tree(l, mid, lson);
    dfs_tree(mid + 1, r, rson);
}

int main()
{
    freopen("ha14d.in", "r", stdin);
    freopen("ha14d.out", "w", stdout);
    int n = read(), T = read();
    while(T --){
        js ++;
        int x = read(), y = read();
        Sec_G(1, n, 1, x, y, js);
    }
    dfs_tree(1, n, 1);
    int answer(0);
    for(int i = 1; i <= 1001; i ++) if(O[i]) answer ++;
    cout << answer;
    return 0;    
}