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#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
using namespace std;
const int maxn = 1E5 + 10;
map<string ,string> mp;
map<string ,string > mp2;
void change(string str1,string str2)
{
if(mp2.count(str1) == 0){
mp[str1] = str2;
mp2[str2] = str1;
}else {
mp[ mp2[str1] ] = str2;
mp2[str2] = mp2[str1];
}
}
int main()
{
int t;
scanf("%d",&t);
string str1,str2;
while(t--){
cin>>str1>>str2;
change(str1,str2);
}
map<string ,string >::iterator it;
cout<<mp.size()<<endl;
for(it = mp.begin();it != mp.end();it++)
cout<<it->first << " "<<it->second<<endl;
return 0;
}
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