//uva1644 #include <stdio.h> #define SIZE 1300000 int t[SIZE] = {0}; int main(void) { int i, j, n, gap; t[0] = t[1] = 1; for (i = 2; i < SIZE; i++) { if(t[i] == 0) { for(j = i+i; j < SIZE; j += i) t[j] = 1; } } while (scanf("%d", &n) && n != 0) { gap = 0; for (i = n; t[i] != 0; i--) gap++; for (i = n; t[i] != 0; i++) gap++; printf("%d\n", gap); } return 0; }