题解

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    double n;
    string s;
    cin>>n>>s;
    if(s=="in"){
        printf("%.2f",n*2.54);
        cout<<" cm";
    }else if(s=="cm"){
        printf("%.2f",n/2.54);
        cout<<" in";
    }else{
        cout<<"error";
    }
    return 0;
}