we can use the netflow algorithm(+ operator) to solve this problem.
#include <cstdio>
#include <cstring>
#include <algorithm>
#define MAXN 5
using namespace std;
const int INF=1<<30;
int n,m,flow[MAXN][MAXN],pre[MAXN],cur[MAXN],gap[MAXN],d[MAXN],g[MAXN],l[MAXN][MAXN];
int Maxflow_Isap(int s,int t,int n) {
memset(d,-1,sizeof(d));
memset(pre,-1,sizeof(pre));
memset(gap,0,sizeof(gap));
gap[s]=n;
int u=pre[s]=s,v,maxflow=0;
while (d[s]<n) {
v=n+1;
for (int i=cur[u];i<=g[u];i++)
if (flow[u][l[u][i]] && d[u]==d[l[u][i]]+1) {
v=l[u][i];cur[u]=i;break;
}
if (v<=n) {
pre[v]=u;u=v;
if (v==t) {
int dflow=INF;u=s;
for (int i=v;i!=s;i=pre[i]) dflow=min(dflow,flow[pre[i]][i]);
maxflow+=dflow;
for (int i=v;i!=s;i=pre[i]) {
flow[pre[i]][i]-=dflow;
flow[i][pre[i]]+=dflow;
}
}
}
else{
int mindist=n;
for (int i=1;i<=g[u];i++)
if (flow[u][l[u][i]]) mindist=min(mindist,d[l[u][i]]);
if (!--gap[d[u]]) return maxflow;
gap[d[u]=mindist+1]++;cur[u]=1;
u=pre[u];
}
}
return maxflow;
}
void setsize(int x,int y,int c) {
flow[x][y]=c;
l[x][++g[x]]=y;
l[y][++g[y]]=x;
}
int main() {
scanf("%d%d",&n,&m);
setsize(1,2,n);
setsize(2,4,n);
setsize(1,3,m);
setsize(3,4,m);
printf("%d\n",Maxflow_Isap(1,4,4));
return 0;
}
