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@@ -0,0 +1,32 @@
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+//
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+// Created by jal on 2019-05-01.
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+//
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+
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+#include<bits/stdc++.h>
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+using namespace std;
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+int main(){
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+ int l,r;
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+ cin >> l >> r;
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+ int n = r - l + 1;
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+ vector<bool>a(n, true);
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+ vector<int>prime;
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+ int m = sqrt(r);
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+ vector<bool>f(m+1, true);
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+ for(int i = 2; i <= m; i++){
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+ if(f[i]){
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+ prime.push_back(i);
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+ }
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+ for(int j = 0; j < prime.size() && prime[j]*i <= m; j++){
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+ f[prime[j]*i] = false;
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+ }
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+ }
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+ for(int i = 0; i < prime.size(); i ++){
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+ int k = prime[i];
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+ for(int j = max(2, (l + k - 1) / k * k); j <= r; j+= k){
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+ a[j-l] = false;
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+ }
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+ }
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+ cout << accumulate(a.begin(), a.end(), 0) << endl;
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+}
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+
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+//2100000000 2101000000
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