1 #include<iostream>
2 #include<cstdio>
3 #include<cstdlib>
4 #include<cstring>
5 #include<string>
6 #include<queue>
7 #include<algorithm>
8 #include<map>
9 #include<iomanip>
10 #include<climits>
11 #include<string.h>
12 #include<numeric>
13 #include<cmath>
14 #include<stdlib.h>
15 #include<vector>
16 #include<stack>
17 #include<set>
18 #define INF 1e7
19 #define MAXN 100010
20 #define maxn 1000010
21 #define Mod 1000007
22 #define N 1299800
23 using namespace std;
24 typedef long long LL;
25
26 int prime[N];
27 int vis[N];
28 void run()
29 {
30 int k = 1;
31 for (LL i = 2; i <= N; ++i)
32 if (!vis[i]) {
33 prime[k++] = i;
34 for (LL j = i*i; j < N; j += i)
35 vis[j] = 1;
36 }
37 /*for (int i = 1; i < 1300; ++i)
38 cout << prime[i] << " ";
39 cout << endl;*/
40 }
41
42 int n;
43 int ans = 0;
44
45 int main()
46 {
47 run();
48 while (cin >> n,n) {
49 ans = 2;
50 if (vis[n] == 0)
51 ans = 0;
52 else {
53 int tmp = n;
54 while (--tmp)
55 if (vis[tmp])
56 ans++;
57 else break;
58 tmp = n;
59 while (++tmp)
60 if (vis[tmp])
61 ans++;
62 else break;
63 }
64 cout << ans << endl;
65 }
66 return 0;
67 }
