### Finding Primes

given below code is for findprm or finding primes spoj .

Here I have applied basic sieve to find primes . Here you have to tell the numbers of prime between N/2 and N . because all primes before N/2 are not common with second sieve(stated in question).

#include <bits/stdc++.h> using namespace std; bool primes[10000009]; int cum[10000009]; void pre(){ for(int i = 3 ; i<= 3163 ; i+=2){ if(!primes[i]){ for(int j = i*i ; j<= 10000000 ; j+=2*i) primes[j] = 1; } } cum[2] = 1; for(int i = 3 ; i<=10000000 ; i++){ if(primes[i] == 0 && i%2 != 0) cum[i] += cum[i-1] + 1; else cum[i] = cum[i-1]; } } int main(){ int t; pre(); scanf("%d",&t); while(t--){ int n; scanf("%d",&n); printf("%d\n" , cum[n] - cum[(n>>1)]); } return 0; }