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 }