uva1644

/**********author:chanjun2016email:[e-mail]***********/#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <vector>#include <string>#include <map>#include <set>#include <algorithm>using namespace std;#define INF = 0x3f3f3f3fconst int maxn = 13e5;int vis[maxn + 10];set<int> S;void init(){int q = sqrt(maxn + 0.5);for (int i = 2;i <= q; ++i){if (!vis[i]){for (int j = i * i; j <= maxn; j += i){vis[j] = 1;}}}for (int i = 2;i <= maxn; ++i){if (!vis[i]){S.insert(i);}}}int main(){int n;init();while (scanf("%d",&n),n > 0){auto begin = lower_bound(S.begin(),S.end(),n);if (*begin == n){printf("0\n");}else{auto end = *begin;printf("%d\n",  end - *--begin);} }return 0;}