函数解法

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll sb;
bool isp(ll x){
for(ll i=2;i<x/i;i++){
if(x % i == 0){
return 0;
}
}
return 1;
}
int main(){
cin >> sb;
if(sb < 1){
cout << "No" << endl;
}else if(isp(sb)){
cout << "Yes" << endl;
}else{
cout << "No" << endl;
}
return 0;
}