a,b,c=map(int,input().split())
ans =0
print((a+b-1)*(c-1)+a*b)#include <iostream>
using namespace std;
int main()
{
int a, b, c;
cin >> a >> b >> c;
cout << a * b + b * c + c * a - a - b - c + 1 << endl;
return 0;
}
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