#include<cstdio>
int t,m,ans;
int time[1010],money[1010];
int dp[10000010];
int max(int a,int b){
	return a>b?a:b;
}
int main(){
	scanf("%d%d",&t,&m);
	for(int i=1;i<=m;i++){
		scanf("%d%d",&time[i],&money[i]);
	}
	for(int i=1;i<=m;++i){
		for(int j=0;j<=t;++j){
			if(j>=time[i]) dp[j]=max(dp[j],dp[j-time[i]]+money[i]);
		}
	}
	printf("%d",dp[t]);
	return 0;
}