#include <stdint.h>
#include <stdio.h>

int main(int argc, char **argv) {
  int g, t, n;
  scanf("%d %d %d", &g, &t, &n);
  int sum = 0;
  for (int i=0; i<n; i++) {
    int a;
    scanf("%d", &a);
    sum += a;
  }
  int lol = (g-t) * 9/10;
  printf("%d\n", lol-sum);
  return 0;
}