DN07

import java.util.*;
public class DN07_63140176{
	public static void main (String [] arg){
		Scanner sc = new Scanner(System.in);
		int v = sc.nextInt();
		int s = sc.nextInt();
		int tab [][] = new int [v][s];
		int [][] tab2 = new int [v][s];
		String a = "";


		String b = sc.nextLine();
		while(sc.hasNextLine()){
			for(int i = 0; i<v;i++){
				a = sc.nextLine();
				//System.out.println(""+a);
				//a = a.concat(String.valueOf(sc.nextInt()));
				for(int j = 0; j<s;j++){

					tab[i][j] = Character.getNumericValue(a.charAt(j));
				}
			}

		}
		//System.out.println(""+a);
		/*for(int i = 0;i<v;i++){
			for(int j = 0;j<s;j++)
				System.out.print(tab[i][j] + " ");
			System.out.println();
			}

		//int t[] = new int [50];
		/*int f = 0;
		for(int i = 0;i<tab.length*tab[0].length ;i++){
			tab2 = vrniCrko(tab,tab2,i+1);
			if(tab2[0][0][1]!=0)
			//f = f+t[i];
			f++;
			else break;
			//if(t[i] != 0) i = t.length;
		}

		/*for(int i = 0;i<v;i++){
			for(int j = 0;j<s;j++)
				System.out.print(tab2[i][j][0] + " ");
			System.out.println();
			}*/

		System.out.println(vrniCrko(tab,tab2));
	}



	public static int vrniCrko(int tab[][],int tab2[][]){
	int g = 0;
	int f = 0;
	int a = 1;
	int bla =0;
	int bla2 =0;
	int stI = 0;
	int stJ = 0;
	/*for(int i = 0;i<tab.length;i++){
			for(int j = 0;j<tab[0].length;j++)
				System.out.print(tab[i][j] + " ");
			System.out.println();}*/
		for(int h = 0;h<tab.length*tab[0].length;h++){
			g=0;

			//a = h+1;
			//System.out.println();

			for(int i = stI; i<tab.length;i++){
			bla = 0;
			bla2=0;
			f = a;
				for(int j = stJ; j<tab[0].length;j++){
				stJ=0;
					/*if(g==0 &&tab[i][j]==1){
					g++;
					tab2[i][j] = a;
					System.out.println("    a   --> " + a   +  "       g-->   " + g  + "      i---> " +i + "    j-->  " + j+ "      g==0 ");
					}*/
					if(tab[i][j] == 1 ){
						if(tab2[i][j]==0){
							tab2[i][j]=a;
							g++;}
						if(tab2[i][j] == a || tab2[i][j] == 0){
							if (j!=tab[0].length-1 && i!=tab.length-1){
								if(tab[i+1][j]==1){
									if(tab2[i+1][j] == a || tab2[i+1][j] ==0){
										g++;
										tab2[i+1][j]=a;
									}

								}
								if(tab[i][j+1]==1){
									if(tab2[i][j+1] ==0 || tab2[i][j+1] ==a){
									g++;
									tab2[i][j+1]=a;
									}


								}
								if(tab[i+1][j] ==0 && tab[i][j+1] ==0){
								a++;
								//System.out.println("tab2["+i+"]["+j+"]     "+tab2[i][j]);
								stI = i;
								if(j != tab[0].length-1)
								stJ = j+1;
								else stJ = 0;
								i=tab.length-1;
								j=tab[0].length-1;
								}
							}

					/*else if (i!=tab.length){
						if(tab[i+1][j]==1 && tab2[i+1][j] ==0){
							g++;
							tab2[i+1][j]=a;
							}
						else if(tab[i][j+1]==1 && tab2[i][j+1] ==0){
							g++;
							tab2[i][j+1]=a;
							}
						}*/
						else if (i==0 && j==tab[0].length-1){
							if(tab[i+1][j]==1){
								if(tab2[i+1][j] == a || tab2[i+1][j] ==0){
									g++;
									tab2[i+1][j]=a;
									bla++;
								}
							}

						}
						else if( i==tab.length-1&&j==0){
							if(tab[i][j+1]==1 ){
								if(tab2[i][j+1]==0 || tab2[i][j+1]==a){
									g++;
									tab2[i][j+1]=a;
									bla2++;
								}
							}
						}

						else if(bla==0 && bla2 ==0 && f==a){
						//System.out.println("tab2["+i+"]["+j+"]     "+tab2[i][j] +"    aegaeg");
								a++;
								stI = i;
								if(j != tab[0].length-1)
								stJ = j+1;
								else stJ = 0;
								i=tab.length-1;
								j=tab[0].length-1;
								}
						else if(i ==tab.length-1 && j == tab[0].length-1){
							if(tab[i][j]==1){
								if(tab2[i][j] ==0 ||tab2[i][j]==a){
									g++;
									tab2[i][j]=a;

								}
							}
						}
						}
					}
					//System.out.println("    a   --> " + a   +  "       g-->   " + g  + "      i---> " +i + "    j-->  " + j + "   tab2["+i+"]["+j+"]  " + tab2[i][j]);
					//System.out.print(tab2[i][j] + " ");
				}
				//System.out.println("    " + i);
				//bla = h;
				//bla2 = j;
			}

			//System.out.print((i+1)+ "-" + g+ "    ");


			if(g==0 && h>=tab.length)
				return a-1;

		}
		//System.out.println();
		/*System.out.println();
		System.out.println();
		for(int i = 0;i<tab2.length;i++){
			for(int j = 0;j<tab2[0].length;j++)
				System.out.print(tab2[i][j] + " ");
			System.out.println();
			}
			System.out.println();
		for(int i = 0;i<tab.length;i++){
			for(int j = 0;j<tab[0].length;j++)
				System.out.print(tab[i][j] + " ");
			System.out.println();
			}*/
		return a-1;
	}
}