题解

#include<bits/stdc++.h>
using namespace std;
int main(){
    string s;
    cin>>s;
    for(int i=0;i<s.size();i++){
        if(s[i]>='A'&&s[i]<='Z') s[i]+=32;
        else if(s[i]>='a' && s[i]<='z') s[i]-=32;
    }
    cout<<s;
}