PairArr removeAt(PairArr arr, int i){
    for(; i<size(arr); i++){
        arr.first[i] = arr.first[i+1];
        arr.second[i] = arr.second[i+1];
    }
    arr.n--;
    return arr;
}

int main(){
    int n=5;
    int connect = 1;

    Arr main = createArr();
    PairArr pending = createPairArr();

    for(int i=0; i<n; i++){
        int from, to;
        cin >> from;
        cin >> to;
        pending = pushPairArr(pending, from, to);
    }

    int prevSize = size(pending);
    for(int i=0; i<size(pending) && prevSize > 0; i++){
        if(contains(main, pending.first[i]) && ! contains(main, pending.second[i])){
            main = pushArr(main, pending.second[i]);
            pending = removeAt(pending, i);
            i--;
        }
        if(contains(main, pending.second[i]) && ! contains(main, pending.first[i])){
            main = pushArr(main, pending.first[i]);
            pending = removeAt(pending, i);
            i--;
        }

        if(prevSize == size(pending)){
            connect = 0;
            break;
        }

        prevSize = size(pending);
    }

    if(connect){
        "yes"
    }
    else{
        "no"
    }

    return 0;
}