#include <bits/stdc++.h>
#define endl "\n"
#define pb push_back
#define int long long
using namespace std;
const int inf = 2e18 + 5;
const int N = 5e3 + 5;
const int mod = 998244353;
int fpow(int a, int b){
if(b == 0) return 1;
int p = 1;
while(b){
if(b&1) p = p*a;
b = b/2;
a = a*a;
}
return p;
}
int32_t main(){
//freopen("in.txt","r", stdin);
int n, m;
cin>>n>>m;
vector<vector<int> > a(n, vector<int>(m));
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
char c;
cin>>c;
a[i][j] = c - '0';
}
}
int ans1 = 0, ans2 = 0;
for(int i = 0; i < n; i++){
bool mask = 0;
for(int j = 0; j < m; j++){
if(a[i][j] == 0 && !mask){
mask = 1;
ans1++;
}
else if(a[i][j] == 1 && mask){
mask = 0;
}
}
}
for(int i = 0; i < m; i++){
bool mask = 0;
for(int j = 0; j < n; j++){
if(a[j][i] == 0 && !mask){
mask = 1;
ans2++;
}
else if(a[j][i] == 1 && mask){
mask = 0;
}
}
}
cout<<min(ans1, ans2)<<endl;
return 0;
}
