请教开心的金明超时问题=w=

#include<stdio.h>
#include<string.h>
int s[30001];
int main()
{freopen("happy.in","r",stdin)
; //freopen("happy.out","w",stdout);
memset(s,0,sizeof(s));
int i,j;
int N,m;
int v,p;
scanf("%d %d",&N,&m);
for(i=1;i<=m;i++)
{scanf("%d %d",&v,&p);for(j=N;j>=v;j--)
{if(s[j-v]+v*p>s[j]) s[j]=s[j-v]+v*p;}}
printf("%d",s[N]);
return 0;}