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Cod sursa(job #797225)
#include <fstream>
using namespace std;
int main()
{ ifstream f("ciur.in");
ofstream g("ciur.out");
int n,cnt = 1,prim[2000002];
f >> n;
for(i = 2;i <= n;i++)prim[i] = 1;
for(i = 3;i <= n;i=i+2){
if(prim[i] == 1){cnt++;
for(j = 2;j*i <= n;j++;prim[i*j] = 0;
}
}
g << cnt;
f.close();
g.close();
return 0;
}