uva 10763

#include<cstdio>#include<cstring>using namespace std;int d[1010][1010];int ok(int n){for(int i=0;i<500;i++)for(int j=0;j<500;j++)if(d[i][j])return 0;return 1;} int main(){int n;while(~scanf("%d",&n)&&n){memset(d,0,sizeof(d));for(int i=0;i<n;i++){int a,b;scanf("%d%d",&a,&b);d[a][b]++;d[b][a]--;}if(n&1)printf("NO\n");else if(ok(n))printf("YES\n");elseprintf("NO\n");}}