Cod sursa(job #2251101)
Utilizator | Macovei Rares-Stefan RaresMacovei | Data | 1 octombrie 2018 09:46:07 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 30 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.5 kb |
#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool ciur[2000001];
int v[2000001];
void Ciur(int n){
int i,j;
ciur[0]=1,ciur[1]=1;
for(i=4;i<=n;i+=2) ciur[i]=1;
for(i=3;i*i<=n;i+=2)
for(j=i*i;j<=n;j+=2*i) ciur[j]=1;
}
int main()
{
int n,i;
fin>>n;
Ciur(n);
v[1]=0;
for(i=2;i<=n;++i){
if(ciur[i]==0) v[i]=v[i-1]+1;
else v[i]=v[i-1];
}
fout<<v[n];
return 0;
}