Problem:
Score : 300 points

Problem Statement

You are given a string S consisting of lowercase English letters.
Another string T is initially empty.
Determine whether it is possible to obtain S = T by performing the following operation an arbitrary number of times:

Append one of the following at the end of T: dream, dreamer, erase and eraser.

Constraints

1≦|S|≦10^5

S consists of lowercase English letters.

Input

The input is given from Standard Input in the following format:

S

Output

If it is possible to obtain S = T, print YES. Otherwise, print NO.

Sample Input 1

erasedream

Sample Output 1

YES

Append erase and dream at the end of T in this order, to obtain S = T.

Sample Input 2

dreameraser

Sample Output 2

YES

Append dream and eraser at the end of T in this order, to obtain S = T.

Sample Input 3

dreamerer

Sample Output 3

NO

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
 
int main() {
  char *buf=(char*)malloc(sizeof(char) * 20000);
 
  scanf("%[^\n]", buf);
  char* cur = buf;
  int length = strlen(buf);
 
  char l1[] = "dream";
  char l2[] = "dreamer";
  char l3[] = "erase";
  char l4[] = "eraser";
  int a1 = 5;
  int a2 = 7;
  int a3 = 5;
  int a4 = 6;
 
  while (length > 0) {
    if (strstr(cur, l4) == cur) {
      length -= a4;
      if(length <= 0) {
        break;
      }
      cur = cur + a4;
    } else if (strstr(cur, l3) == cur) {
      length -= a3;
      if(length <= 0) {
        break;
      }
      cur = cur + a3;
    } else if (strstr(cur, "dreamerase") == cur) {
      length -= a1;
      if(length <= 0) {
        break;
      }
      cur = cur + a1;
    } else if (strstr(cur, l2) == cur) {
      length -= a2;
      if(length <= 0) {
        break;
      }
      cur = cur + a2;
    } else if (strstr(cur, l1) == cur) {
      length -= a1;
      if(length <= 0) {
        break;
      }
      cur = cur + a1;
    } else {
      break;
    }
  }
 
  if (length == 0) {
    printf("YES\n");
  } else {
    printf("NO\n");
  }
 
  return 0;
}