#include <bits/stdc++.h>
using namespace std;
int a[110],b[110];
double z[110];

int main()
{
    //freopen("caiyao.in","r",stdin);
    //freopen("caiyao.out","w",stdout);
    int t,m,ans = 0;
    scanf("%d%d",&t,&m);
    for(int i = 1;i <= m;i ++) scanf("%d%d",&a[i],&b[i]);
    for(int i = 1;i <= m;i ++) z[i] = b[i] / a[i];
    sort(z + 1,z + m + 1);
 
    for(int i = 1;i <= m;i ++){
        if(t == 0) break;
        if(a[i] > t) continue;

        ans += b[i];
        t -= b[i];
    }
    printf("%d\n",ans);

    return 0;
}