/*
TASK:matrix
LANG:C++
*/

# include <iostream.h>
# include <stdlib.h>

int m,n;
int a[300][100];

int main()
{int i,j;
 cin>>n>>m;
 for (i=0;i<n;i++)
 for (j=0;j<m;j++) cin>>a[i][j];
 cout<<(m+n)/3;
 return 0;
}
