#include <stdio.h>

int load, len, n, rows;
int koko;

typedef struct {
  int w, s;
} vehicle;

double pole[1010][1010];
int mins[1010][1010];
int valmins[1010][1010];
int prefix[1010];
vehicle vehs[1010];

void Prefix() {
    prefix[0] = vehs[0].w;
    for(int i = 1; i < n; i++) {
	prefix[i] = prefix[i-1]+vehs[i].w;
    }
}

void Print() {
//    for(int i = 0; i < n; i++)
//	printf("* %d ", prefix[i]);
    for(int i = 0; i < rows; i++) {
	for(int j = 0; j < n; j++)
	    printf("%5.2f ", pole[i][j]);
	printf("\n");
    }
    printf("\n");
}

int MinSpeed(int from, int to) {
    if (valmins[from][to] == koko) return mins[from][to];
    else {
    int min = -1;
    for(int i = from; i <= to; i++) {
	if (min == -1 || min > vehs[i].s) min = vehs[i].s;
    }
    valmins[from][to] = koko;
    mins[from][to] = min;
    return min;
    }
}

double Solve() {
    int i = 0;
    for(i = 0; i < n; i++) {
	if (prefix[i] > load)
	    pole[0][i] = 0;
	else
	    pole[0][i] = len / (double)MinSpeed(0, i)*60;
    }
    rows++;
//    Print();
    if (pole[0][n-1] != 0)
        return pole[0][n-1];
    i = 1;
    int gw;
    int minsp;
    double time;
    for(i = 1; i < n; i++) {
	for(int j = i; j < n; j++) {
	    pole[i][j] = 0;
	    for(int k = i-1; k < j; k++) {
//		printf("F: %.1f S: %d\n", pole[i-1][k], prefix[j]-prefix[k]);
//		printf("Sec: j %d k %d\n", j, k);
		if (prefix[j] - prefix[k] > load) continue;
		if (pole[i-1][k] == 0) 
		    if (prefix[j] - prefix[k] > load)
			continue;
		    else
			break;
		gw = prefix[j] - prefix[k];
		minsp = MinSpeed(k+1, j);
		time = (len / (double)minsp)*60;
//		printf("Time: %5.2f %5.2f %5.2f\n", pole[i-1][k], time, pole[i][j]);
		if (pole[i][j] == 0 || pole[i][j] > time + pole[i-1][k])
		    pole[i][j] = time + pole[i-1][k];
	    }
	}
	rows++;
//	Print();
//	if (rows == 2) return -1;
	if (pole[i][n-1] != 0)
	    return pole[i][n-1];
    }
//    Print();
    return -1;
}

int main() {
    koko = 1;
    scanf("%d %d %d\n", &load, &len, &n);
    while(load != 0 || len != 0 || n != 0) {
	for(int i = 0; i < n; i++) {
	    scanf("%d %d\n", &vehs[i].w, &vehs[i].s);
	}
	rows = 0;
	Prefix();
	double time = Solve();
	printf("%.1f\n", time);
	koko++;
	scanf("%d %d %d\n", &load, &len, &n);
    }
    return 0;
}