#include <cstdio>

#include <cstring>

#include <cmath>

#include <string>

#include <iostream>

#include <algorithm>

#include <queue>

using namespace std;

#define rep(i, n) for(int i=0; i<(n); ++i)

#define for1(i,a,n) for(int i=(a);i<=(n);++i)

#define for2(i,a,n) for(int i=(a);i<(n);++i)

#define for3(i,a,n) for(int i=(a);i>=(n);--i)

#define for4(i,a,n) for(int i=(a);i>(n);--i)

#define CC(i,a) memset(i,a,sizeof(i))

#define read(a) a=getint()

#define print(a) printf("%d", a)

#define dbg(x) cout << #x << " = " << x << endl

#define printarr(a, n, m) rep(aaa, n) { rep(bbb, m) cout << a[aaa][bbb]; cout << endl; }

inline const int getint() { int r=0, k=1; char c=getchar(); for(; c<'0'||c>'9'; c=getchar()) if(c=='-') k=-1; for(; c>='0'&&c<='9'; c=getchar()) r=r*10+c-'0'; return k*r; }

inline const int max(const int &a, const int &b) { return a>b?a:b; }

inline const int min(const int &a, const int &b) { return a<b?a:b; }

struct dat { int x, y; }a[50005];

int n;

bool cmp(const dat &a, const dat &b) { return a.y<b.y; }

int main() {

    read(n);

    for1(i, 1, n) read(a[i].x), read(a[i].y);

    sort(a+1, a+1+n, cmp);

    int ans=0, ed=0;

    for1(i, 1, n) {

        if(a[i].x>=ed) {

            ++ans;

            ed=a[i].y;

        }

    }

    print(ans);

    return 0;

}

第1，3，4共3只奶牛可以同时吃草，第1，3，5也可以．

Silver