#include <stdio.h>
#include <algorithm>
bool v[3000][3000];
int ps[3000],ps2[3000];
int lines[3000];
int main(){
    int n,m,i,j,cnt = 0,res;
    char ch;
    scanf("%d%d\n",&n,&m);
    if(m%2 == 1){
        for(i = 0;i < n;i++)for(j = 0;j < m;j++){
            scanf("%c",&ch);v[j][i] = ch - '1';
            scanf("%c",&ch);
        }
        res = n;n = m;m = res;
    }else for(i = 0;i < n;i++)for(j = 0;j < m;j++){
        scanf("%c",&ch);v[i][j] = ch - '1';
        scanf("%c",&ch);
    }
    if(n == 1){
        for(i = 0;i < n;i++){
            for(j = 0;j < m;j++){
                cnt+=v[i][j];
            }
        }
        if(cnt == n*m){
            printf("1");
        }else if(cnt == 0){
            printf("0");
        }else printf("-1");
    }else if(n%2 == 0){
        for(i = 0;i < n;i++){
            for(j = 0;j < m;j++){
                ps[i]+=v[i][j];
                ps2[j]+=v[i][j];
            }
        }
        for(i = 0;i < n;i++){
            for(j = 0;j < m;j++){
                cnt+=((ps[i] + ps2[j] + v[i][j])%2);
            }
        }
        printf("%d",cnt);
    }else{
        int cnt2 = 0;
        for(i = 0;i < n;i++){
            for(j = 0;j < m;j++){
                if(i == n - 1){
                    cnt2+=(v[i][j] == cnt);
                }else{
                    v[n - 1][j]^=v[i][j];
                    cnt+=v[i][j];cnt%=2;
                    ps[i]+=v[i][j];ps2[j]+=v[i][j];
                }
            }
        }
        if(cnt2 != 0 && cnt2 != m){
            printf("-1");
        }else{
            for(i = 0;i < n - 1;i++){
                for(j = 0;j < m;j++){
                    lines[j]+=(v[i][j]+ps[i]+ps2[j])%2;
                }
            }
            if(cnt2 == 0)for(j = 0;j < m;j++)lines[j]++;
            std::sort(lines,lines + m);
            int sum = 0,ans;
            for(i = m-1;i >= 0;i--)sum+=lines[i];
            if(cnt2 == 0)sum-=lines[m - 1];lines[m - 1] = n - lines[m - 1];sum+=lines[m - 1];
            ans = sum;
            for(i = m-2;i >= 0;i-=2){
                sum-=lines[i];sum-=lines[i - 1];
                lines[i] = n - lines[i];
                lines[i - 1] = n - lines[i - 1];
                sum+=lines[i];sum+=lines[i - 1];
                if(ans > sum)ans = sum;
            }
            printf("%d",ans);
        }
    }
    return 0;
}
/**
3 4
1 2 1 2
1 1 2 2
2 1 1 2
3 4
2 2 2 2
2 2 2 2
2 2 2 2
**/