1007

#include<iostream>#include<vector>#include<string>using namespace std;bool ptable[100000];int main(){freopen("in.txt","r",stdin);int n;cin>>n;ptable[0]=ptable[1]=1;int cnt=0;if(n<=2){cout<<0<<endl;return 0;}for(int i=2;i<=n;i++){if(ptable[i]==0){if(ptable[i-2]==0) cnt++;for(int j=2*i;j<=n;j+=i){ptable[j]=1;}}}cout<<cnt<<endl;}