Sieve Of Eratosthenes (Set)

#include<cstdio>
#include<cmath>
#include<cstring>
#include<set>

int main() {
     int n;
     scanf("%d", &n);
     std::set<int> nonprime;
     int limit = sqrt ((double) n);
     nonprime.insert(1);
     for (int i=2; i<=n; i++) {
         if (nonprime.count(i) > 0) continue;
         for (int j=2*i; j<=n; j+=i)
            nonprime.insert(j);
     }
     for (int i=n; i>1; i--) {
         if (nonprime.count(i) == 0) {
             printf("%d\n", i);
             break;
         }
     }
     return 0;
}