#include <stdio.h> #include <math.h> #include <stdlib.h> #define MAX 101 int main(void) { int N = 0; int input[MAX] = {0}; int jumpers[MAX] = {0}; scanf("%d", &N); for (int i = 0; i < N; i++) { scanf("%d", &input[i]); } for (int i = 0; i < N - 1; i++) { int min = abs(input[i] - input[i + 1]); if (min >= N) { printf("NO\n"); return 0; } if (jumpers[min] == 0) { jumpers[min] = 1; } else { printf("NO\n"); return 0; } } printf("YES\n"); return 0; }