Problem 10

The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Find the sum of all the primes below two million.

C++:

#include 
     
      #include 
      
       #include 
       
        using namespace std;const int MAXN = 2000000;bool sieveflag[MAXN+1];void esieve(int n){    // 初始化    memset(sieveflag, true, sizeof(sieveflag));    sieveflag[0] = false;    sieveflag[1] = false;    for(int i=4; i<=n; i+=2)        sieveflag[i] = false;    // 筛选    int max = sqrt(n);    for(int i=3; i<=max; i+=2) {        if(sieveflag[i]) {            for(int j=i+i; j<=n; j+=i)                sieveflag[j] = false;        }    }}int main(){    esieve(MAXN);    int n;    while(cin >> n && n<=MAXN) {        long sum = 2;        for(int i=3; i
       
      
     

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