Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	for {
		n, m := io.NextInt(), io.NextInt()
		if n == 0 {
			break
		}
		p := make([][]int, m)
		for i := 0; i < n; i++ {
			d, v := io.NextInt()-1, io.NextInt()
			p[d] = append(p[d], v)
		}
		sum := 0
		for i := 0; i < m; i++ {
			max := 0
			for _, v := range p[i] {
				max = intMax(v, max)
			}
			sum += max
		}
		io.Println(sum)
	}
}

func intMax(a, b int) int {
	if a < b {
		return b
	}
	return a
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<map>
#include<cstring>
#include<math.h>
#include<bitset>
#include<queue>
#include<set>
#include<iomanip>
#include<math.h>
#include<assert.h>
#include<string>
#include<cstdlib>
#include<cctype>
#include<unordered_map>
#include<sstream>
// #include<bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int,int>;
constexpr ll INF = 1LL<<60;
const double INFD = 1e100;
const ll mod = 1000000007;
const double PI = 3.1415926535897932384626433832795028841971;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
};
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
};

// intやllをstringに変換
template<typename T> inline string toString(const T &a){
  ostringstream oss;
  oss << a;
  return oss.str();
};
// ----------------------------------------------------------------------------

int main(){
  while(1){
  ll N,M;
  cin >> N >> M;
  if(N==0 && M==0){
    break;
  }
  vector<vector<int>> G(M);
  for(int i=0; i<N; i++){
    int d,v;
    cin >> d >> v;
    d--;
    G[d].push_back(v);
  }
  ll sum = 0;
  for(int i=0; i<M; i++){
    sort(G[i].begin(),G[i].end(),greater<int>());
    sum += G[i][0];
  }
  cout << sum << endl;
  }

  return 0;
}

C++: #include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
void solve(int N, int M){
    vector<int> V(M);
    rep(i,0,N){
        int a,b;
        cin >> a >> b;
        a--;
        V[a] = max(V[a], b);
    }
    int sum = 0;
    rep(i,0,M)sum += V[i];
    cout << sum << endl;
}
main(){
    int N,M;
    cin >> N >> M;
    while(N){
        solve(N,M);
        cin >> N >> M;
    }
}

C++: #include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cstring>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <numeric>
#include <functional>
#include <cctype>
#include <list>
#include <limits>
#include <cassert>
//#include <boost/multiprecision/cpp_int.hpp>

const double EPS = (1e-10);


using namespace std;
using Int = long long;
//using namespace boost::multiprecision;

const Int MOD = 1000000007;

long long mod_pow(long long x, long long n) {
    long long res = 1;
    for(int i = 0;i < 60; i++){
        if(n >> i & 1) res = res * x % MOD;
        x = x * x % MOD;
    }
    return res;
}

template<typename T>
T gcd(T a, T b) {
    return b != 0 ? gcd(b, a % b) : a;
}

template<typename T>
T lcm(T a, T b) {
    return a * b / gcd(a, b);
}

void fast_input() {
    cin.tie(0);
    ios::sync_with_stdio(false);
}


int solve(int N, int M) {
    vector<int> problems(M+1);
    int ret = 0;
    for (int i = 0; i < N; i++) {
        int d, v; cin >> d >> v;
        problems[d] = max(problems[d], v);
    }
    for (int i = 1; i <= M; i++) {
        ret += problems[i];
    }
    return ret;
}

int main(void) {
    int N, M;
    vector<int> ans;
    while (1) {
        cin >> N >> M;
        if (!N && !M) break;
        ans.push_back(solve(N, M));
    }
    for (int &i : ans) {
        cout << i << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
#define ll long long
#define INF INT_MAX 
#define mod 1000000007
using namespace std;
int main(){
    ll N,M;
    cin >> N >> M;
    pair<int,int> P[N];
    for(int i=0;i<N;i++){
        cin >> P[i].first >> P[i].second;
    }
    sort(P,P+N);
    int ans = 0;
    int cnt = 0;
    int j=1;
    for(int i=0;i<N;i++){
        cout << P[i].first << " " << P[i].second << endl;
    }
    for(int i=0;i<N;i++){
        if(j==P[i].first){
            cnt = max(cnt,P[i].second);
            if(P[i+1].first!=j){
                j++;
                ans += cnt;
                cnt = 0;
            }
        }
    }
    cout << ans << endl;
}

C++: #include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef complex<double> Point;

#define PI acos(-1.0)
#define EPS 1e-10
const ll INF = 1e16;
const ll MOD = 1e9 + 7;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define rep(i,N) for(int i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define EQ(a,b) (abs((a)-(b))<EPS)
#define EQV(a,b) ( EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()) )
#define fi first
#define se second
#define N_SIZE (1LL << 20)
#define NIL -1

ll mod_add(ll a, ll b) { return (a + b) % MOD; }
ll mod_sub(ll a, ll b) { return (a - b + MOD) % MOD; }
ll mod_mul(ll a, ll b) { return a*b % MOD; }

int n,m;

int main(){
    while(cin >> n >> m&&n){
        vector<ll> cnt(m,0);
        rep(i,n){
            ll d,v;
            cin >> d >> v;
            d--;
            cnt[d] = max(cnt[d],v);
        }
        ll ans = 0;
        rep(i,m)ans += cnt[i];
        cout << ans << endl;
    }
}