C :

#include <stdio.h>
#include <stdlib.h>
#define maxn 30
#define maxv 3010
#define max(A,B) ((A)<(B))?(B):(A)
typedef struct{
int price, value;
}Node;

Node item[maxn];
int dp[maxv];
int main()
{
    int N, M;
    while(scanf("%d%d",&N, &M) != EOF) {
        for(int i = 1;i <= M; i++)scanf("%d%d",&item[i].price,&item[i].value);
        for(int i = 0;i <= N; i++)dp[i]=0;
        for(int i=1; i<= M; i++){
            for(int j = N;j >= item[i].price; j--){
                dp[j]=max(dp[j],dp[j-item[i].price]+item[i].price*item[i].value);
            }
        }
        printf("%d\n",dp[N]);
    }

    return 0;
}

C++ :

#include <bits/stdc++.h>
using namespace std;

int n, m;
int v[30], p[30], f[30009];

int main() {
	cin >> n >> m;
	for (int i = 1; i <= m; i ++) cin >> v[i] >> p[i];
	
	for (int i = 1; i <= m; i ++) {
		for (int j = n; j >= v[i]; j --) {
			f[j] = max(f[j], f[j - v[i]] + v[i] * p[i]);
		}
	}
	cout << f[n];

	return 0;
}