#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
long int solve(int n, int m){
// Complete this function
// The Square is m x n
long int step = 0;
while (m>1){
step++;
m--;
}
while (n>1){
step++;
n--;
}
return step;
}
int main() {
long int n;
long int m;
cin >> n >> m;
long int result = solve(n, m);
cout << result << endl;
return 0;
}
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