#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>
#define nn "\n"
#define x_x ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define intt int _; cin >> _; while (_--)
#define emp push_back
#define mod 1000000007
#define all(v) v.begin(), v.end()
#define ld long double
#define A first
#define B second
typedef long long ll;
const ld eps = 1e-27;
// diff between decimals 0.000000001 mt19937 mt(time(nullptr));
int fx[]={1,-1,0,0}, fy[]={0,0,1,-1};
int main() {
/*freopen("measurement.in","r",stdin);
freopen("measurement.out","w", stdout);*/
x_x
int m,n; cin>>m>>n; pair<ll,int>ar[n]; int mtch[7]={}; mtch[6]=m;
for(auto&i:ar) cin>>i.A>>i.B;
sort(ar, ar+n, greater<pair<ll,int>>());
ll ans=0;
for (int i=0; i<n; i++) {
int nw[7]={};
for (int j=6; j>=1&&ar[i].B; --j) {
if (!mtch[j]) { continue;}
ll x=min(mtch[j],ar[i].B); ar[i].B-=x, mtch[j]-=x; nw[j-1]+=x;
ans+=(x*ar[i].A);
}
for (int j=1; j<7; j++)mtch[j]+=nw[j];
}
cout<<ans;
return 0;
}
