int@h,@w;
string@c[h];
int d[h*2-1][w*2-1];
d[0][0]=0;
rep(i,1,(h+w)*2-3){
	rep(y,h*2-1){
		int x=i-y;
		if(0<=x<w*2-1){
			int z=int_inf;
			if(y&x&1){
				z=min(d[y-1][x],d[y][x-1])+1;
			}else if(y&1){
				if(c[y>>1][x>>1]!='#'){
					z=d[y-1][x]+1;
				}
				if(x){
					z<?=min(d[y][x-1],d[y][x-2])+1;
				}
			}else if(x&1){
				if(c[y>>1][x>>1]!='#'){
					z=d[y][x-1]+1;
				}
				if(y){
					z<?=min(d[y-2][x],d[y-1][x])+1;
				}
			}else{
				if(y){
					z=d[y-1][x]+1;
					if(c[y-2>>1][x>>1]!='#'){
						z<?=d[y-2][x]+1;
					}
				}
				if(x){
					z=d[y][x-1]+1;
					if(c[y>>1][x-2>>1]!='#'){
						z<?=d[y][x-2]+1;
					}
				}
			}
			d[y][x]=z;
		}
	}
}
wt(d[h*2-2][w*2-2]);