#include
#include
#include
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop /
int main(int argc, char* argv) {
int M,N;
while(cin>>M>>N)
{
if(M==-1 && N==-1)
break;
{ double j[1001];
double f[1001];
double x[1001];
for(int i=0; i
{
cin>>j[i];
cin>>f[i];
}
for(int k=0; k<N; k++) //性价比
{
x[k] = j[k] / f[k];
}
for(int i=0; i<N; i++) //性价比排序
{
for(int k=i+1; k<N; k++)
{
if(x[i]<x[k])
{
double temp = x[i];
x[i] = x[k];
x[k] = temp;
temp = j[i];
j[i] = j[k];
j[k] = temp;
temp = f[i];
f[i] = f[k];
f[k] = temp;
}
}
}
double sum = 0;
for(int i=0; i<N; i++)
{
if(M==0)
break;
for(int k=0; k<f[i]; k++)
{
if(M==0)
break;
sum = sum + x[i];
M--;
}
}
cout<<setiosflags(ios::fixed)<<setprecision(3)<<sum<<endl;
}
}
return 0;
}
