#include <iostream>
#include <iomanip>
#include <algorithm>
#include <cstdio>
#define MAXN 1001

using namespace std;

double m;
int n;
double ans;
struct node
{
    double vw;
    double val;
    double wei;
}a[MAXN];
bool cmp(node a, node b)
{
    if(a.vw != b.vw) return a.vw > b.vw;
    return a.wei < b.wei;
}

int main()
{
    cin >> m >> n;
    for(register int i = 1; i <= n; i++)
    {
        cin >> a[i].val >> a[i].wei;
        a[i].vw = a[i].val / a[i].wei;
    }
    sort(a + 1, a + n + 1, cmp);
    for(register int i = 1; i <= n; i++)
    {
        if(m >= a[i].wei)
        {
            m -= a[i].wei, ans += a[i].val;
        } 
        else
        {
            ans += a[i].vw * m;
            m = 0;
        }
    }
    cout << fixed << setprecision(1) << ans;
    return 0; 
}