题解在此

#include <iostream>
#include <cmath>
using namespace std;
int main(){
    int n;
    cin>>n;
    int cnt=abs(n);
    int ans=0;
    while (cnt){
        ans=ans*10+cnt%10;
        cnt/=10;
    }
    if (n<0){
        cout<<'-';
    }
    cout<<ans;
    return 0;
}