/*
ID: LinKArftc
PROG: 2444.cpp
LANG: C++
*/

#include <map>
#include <set>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <cstdio>
#include <string>
#include <utility>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define eps 1e-8
#define randin srand((unsigned int)time(NULL))
#define input freopen("input.txt","r",stdin)
#define debug(s) cout << "s = " << s << endl;
#define outstars cout << "*************" << endl;
const double PI = acos(-1.0);
const double e = exp(1.0);
const int inf = 0x3f3f3f3f;
const int INF = 0x7fffffff;
typedef long long ll;

const int maxn = 510;
const int maxm = 250010;

int mp[maxn][maxn];
int linker[maxn];
int id[maxn];
int uN, vN;
int n, m;
bool vis[maxn];

bool dfs(int x) {
    for (int i = 1; i <= n; i ++) {
        if (mp[x][i]) {
            if (id[i] == id[x]) return false;
            if (id[i] == 0) {
                id[i] = -1 * id[x];
                if (!dfs(i)) return false;
            }
        }
    }
    return true;
}

bool dfs1(int u) {
    for (int v = 1; v <= n; v ++) {
        if (mp[u][v] && !vis[v]) {
            vis[v] = true;
            if (linker[v] == -1 || dfs1(linker[v])) {//刚开始这地方写成dfs了，罪过呀，写的有点混乱，下次注意！
                linker[v] = u;
                return true;
            }
        }
    }
    return false;
}

int hungry() {
    memset(linker, -1, sizeof(linker));
    int ret = 0;
    for (int i = 1; i <= n; i ++) {
        memset(vis, 0, sizeof(vis));
        if (dfs1(i)) ret ++;
    }
    return ret;
}

int main() {
    //input;
    int u, v;
    while (~scanf("%d %d", &n, &m)) {
        memset(mp, 0, sizeof(mp));
        memset(id, 0, sizeof(id));
        for (int i = 1; i <= m; i ++) {
            scanf("%d %d", &u, &v);
            mp[u][v] = 1;
            mp[v][u] = 1;
        }
        bool flag = true;
        for (int i = 1; i <= n; i ++) {
            if (!id[i]) {
                id[i] = 1;
                if (!dfs(i)) {
                    flag = false;
                    break;
                }
            }
        }
        if (!flag) {
            printf("No\n");
            continue;
        } else printf("%d\n", hungry() / 2);
    }
    return 0;
}