poj2673

简单题

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

int t, x, m;
int n;

void input()
{
    scanf("%d%d%d", &t, &x, &m);
    n = 0x3f3f3f3f;
    for (int i = 0; i < m; i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        n = min(n, (a - 1) / b + 1);
    }
}

void work()
{
    int ans = 0;
    if (n - 1 >= t)
    {
        printf("%d\n", t * x);
        return;
    }
    if (n - 1 == 0)
    {
        printf("0\n");
        return;
    }
    ans += n - 1;
    t -= n - 1;
    ans += t / 2;
    printf("%d\n", ans * x);
}

int main()
{
    //freopen("t.txt", "r", stdin);
    input();
    work();
    return 0;
}