#include<stdio.h>
//用筛选法求素数 
bool p[1299720];
int main()
{
	int k,ans,i,i2;
for(i=0;i<=1299709;i+=2){ p[i]=0; } 
for(i=1;i<=1299709;i+=2){ p[i]=1; } 
p[2]=1;p[1]=0;
for(i=3;i<=1000;i+=2)
{ if(p[i]==1)
{i2=i+i; k=i2+i;
while(k<=1299709)
{p[k]=0;k+=i2;}
}
}
	while(scanf("%d",&k)&&k!=0)
	{
		if(k==1)
		{
			printf("0\n");
			continue;
		}
		if(p[k]==1)
		{
			printf("0\n");
			continue;
		}
		else
		{
			ans=1;
			for(i=k-1;;i--)
			{
				if(p[i]==0)
					ans++;
				else
					break;
			}
			for(i=k+1;;i++)
			{
				if(p[i]==0)
					ans++;
				else
					break;
			}
			printf("%d\n",ans+1);
		}
	}
	return 0;
}/*10
11
27
2
492170
0*/

• Re:wa?? (845) hdjtdxacm 2009-02-19 16:22:14