hdu 2159

#include <stdio.h>
#include <string.h>
int main()
{
     int n ,m ,k ,s ,t ,i ,j ,f[105][105] ,a[105] ,b[105];
     while(scanf("%d %d %d %d",&n ,&m ,&k ,&s) != EOF)
     {
           memset(f ,0 ,sizeof(f));
           for(i = 1 ;i <= k ;i++)
                 scanf("%d %d",&a[i] ,&b[i]);
           for(j = 1 ;j <= s ;j++)
           {
                 for(t = 1 ;t <= m ;t++)
                 {
                        int max = -1;
                        for(i = 1 ;i <= k ;i++)
                        {
                             if(t >= b[i] && f[j - 1][t - b[i]] + a[i] > max)
                             max = f[j - 1][t - b[i]] + a[i];
                        }
                        f[j][t] = max;
                 }
           }
           for(i = 1 ;i <= m ;i++)
                if(f[s][i] >= n) break;
           if(i <= m) printf("%d\n",m - i);
           else printf("-1\n");
     }
     return 0;
}