C :

#include<stdio.h>
void main()
{
	int a,b,t;
	scanf("%d",&b);
	while(scanf("%d",&a)!=EOF)
	{
		if(a<b)
		{
			printf("NO");
			goto L;
		}
		else
		{
			t=a;a=b;b=t;
		}
	}
	printf("YES");
L: ;
}

C++ :

#include <stdio.h>
#define maxSize 1000

bool isSorted(int *arr, int n) {
	int i, j;
	for (i = 0; i < n; ++i) {
		for (j = i+1; j < n; ++j) {
			if (*(arr+i) > *(arr+j)) {
				return false;
			}
		}
	}
	return true;
}

int main() {
	int num, count = 0;
	int arr[maxSize];
	
	while (scanf("%d", &num) != EOF) {
		arr[count++] = num;
	}
	
	bool flag = isSorted(arr, count);

	if (flag) {
		printf("YES\n");
	} else {
		printf("NO\n");
	}

	return 0;
}