30 lines
523 B
C++
30 lines
523 B
C++
#include<cstdio>
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#include<cmath>
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#include<algorithm>
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using namespace std;
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const int maxn=1299709;
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bool vis[maxn+5]={1,1};
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int pri[100005],cnt,n;
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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int m=(int)sqrt(maxn+0.5),c=0,i,j;
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for(i=2;i<=m;i++)
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if(!vis[i])
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for(j=i*i;j<=maxn;j+=i) vis[j]=1;
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for(i=2;i<=maxn;i++)
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if(!vis[i]) pri[cnt++]=i;
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while(scanf("%d",&n)==1&&n)
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{
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if(!vis[n]) printf("0\n");
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else
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{
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int *p=upper_bound(pri,pri+cnt,n);
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printf("%d\n",*p-*(p-1));
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}
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}
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return 0;
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}
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