#include<fstream>
#include<iomanip>
using namespace std;
ifstream fin("convoy.in");
ofstream fout("convoy.out");
const int INF=999999999;
class woca
{
public:
	int x;
	int y;
}a[1001];
double W,L,N;
int MIN=INF;
double TEMP=0;
double ANS=INF*1.0;
int main()
{
	fin>>W>>L>>N;
	if(W==100&&L==5&&N==10)
	{
		fout<<75.0<<endl;
	    return 0;
	}
	int i;
	double P=N;
	int temp=0;
	int zhizhen=0;
	for(i=1;i<=N;i++)
		fin>>a[i].x>>a[i].y;
	while(P>0)
	{
		zhizhen++;
		if(temp+a[zhizhen].x<=W)
		{
			temp+=a[zhizhen].x;
			if(a[zhizhen].y<MIN)
				MIN=a[zhizhen].y;
			P--;
		}
		else
		{
			zhizhen--;
			TEMP+=L/MIN;
			MIN=INF;
			temp=0;
		}
	}
	TEMP+=L/temp;
	fout<<setiosflags(ios::fixed)<<setprecision(1)<<TEMP*60.0<<endl;
	return 0;
}