41 lines
742 B
C++
41 lines
742 B
C++
#include <iostream>
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#include <stdio.h>
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using namespace std;
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long long ans=0x3f3f3f3f3f3f3f;
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void dfs(long long L,long long R,long long RR)
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{
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if(L<0||R>2*RR)
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return;
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if(ans&&ans<=R)
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return;
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if(L==0)
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{
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ans=min(ans,R);
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return;
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}
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if (2*L<R+1)
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return;
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dfs(2*L-R-1,R,RR);
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dfs(2*L-R-2,R,RR);
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dfs(L,2*R-L+1,RR);
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dfs(L,2*R-L,RR);
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}
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int main()
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{
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long long L,R;
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while(~scanf("%I64d %I64d",&L,&R))
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{
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dfs(L,R,R);
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if(ans==0x3f3f3f3f3f3f3f)
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{
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printf("-1\n");
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}
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else
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{
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printf("%I64d\n",ans);
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}
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ans=0x3f3f3f3f3f3f3f;
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}
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return 0;
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}
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