(n, m) = map(int, input().split(' '))
all = []
for i in range(m):
(a, b) = map(int, input().split(' '))
all.append([a, b])
all.sort(key=lambda x:x[1])
all.reverse()
matches = 0
for sublist in all:
if sublist[0] < n:
matches += sublist[1] * sublist[0]
n -= sublist[0]
else:
matches += n * sublist[1]
break
print(matches)#include <bits/stdc++.h>
using namespace std;
#define en "\n"
#define ll long long
struct node{
ll a;
int b;
};
bool comp(node a, node b){
return a.b < b.b;
}
int main()
{
ll n;
int m;
cin>>n>>m;
vector <node> v;
while (m--){
ll a;
int b;
cin>>a>>b;
node c;
c.a = a;
c.b = b;
v.push_back(c);
}
sort(v.begin(), v.end(), comp);
ll sum=0;
for (int i=v.size()-1;n>0 && i>=0;i--){
if(v[i].a <= n){
sum += (v[i].b * v[i].a);
n-=v[i].a;
}
else if (n < v[i].a){
sum += (v[i].b * n);
break;
}
}
cout<<sum;
return 0;
}148A - Insomnia cure | 1650A - Deletions of Two Adjacent Letters |
1512A - Spy Detected | 282A - Bit++ |
69A - Young Physicist | 1651A - Playoff |
734A - Anton and Danik | 1300B - Assigning to Classes |
1647A - Madoka and Math Dad | 710A - King Moves |
1131A - Sea Battle | 118A - String Task |
236A - Boy or Girl | 271A - Beautiful Year |
520B - Two Buttons | 231A - Team |
479C - Exams | 1030A - In Search of an Easy Problem |
158A - Next Round | 71A - Way Too Long Words |
160A - Twins | 1A - Theatre Square |
1614B - Divan and a New Project | 791A - Bear and Big Brother |
1452A - Robot Program | 344A - Magnets |
96A - Football | 702B - Powers of Two |
1036A - Function Height | 443A - Anton and Letters |