ACM 10038 -- Jolly Jumpers

#include <stdio.h>
#include <math.h>


int main(int argc, char* argv[])
{
    int counter;
    int num[3000];
    int flag[3000];

    while( scanf("%d", &counter) == 1 ){
        int i;
 for(i = 0 ; i < counter ; i++){
            scanf("%d", &num[i]);
            flag[i] = 0;
        }

        int res = 0;
        for(i = 1 ; i < counter ; i++){
            int diff;
            if(num[i] > num[i-1]){
                diff = num[i] - num[i-1];
            }else{
                diff = num[i-1] - num[i];
            }

            if(0 < diff && diff < counter){
                if(flag[diff] == 0){
                    flag[diff] = 1;
                }else{
                    res = 1;
                    break;
                }
            }else{
                res = 1;
                break;
            }

        }

        if( res == 1 ){
            printf("Not jolly\n");
        }
        else{
            printf("Jolly\n");
        }
    }
 return 0;
}