28 lines
318 B
C++
28 lines
318 B
C++
#include<cstdio>
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#include<cstring>
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int n;
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bool isp[1000005];
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void solve()
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{
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int p=0,i,j;
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for(i=2;i<=n;i++)
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if(isp[i])
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{
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p++;
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for(j=2;j*i<=n;j++) isp[j*i]=0;
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}
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printf("%d\n",p);
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}
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void init()
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{
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scanf("%d",&n);
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memset(isp,1,sizeof(isp));
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isp[0]=isp[1]=0;
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}
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int main()
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{
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init();
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solve();
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return 0;
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}
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